After lying dormant for more than 40 years, one of MLB’s most heated postseason rivalries is being rekindled.

With the Royals’ victory over Baltimore in AL Wild Card Series Game 2 on Wednesday, Kansas City moves forward to face the Yankees in the ALDS. It’s a matchup with a lot of history that may be lost on many fans, but from the mid-1970s through the early ‘80s, these franchises met in the postseason four times in five years and contributed some of the sport’s most memorable moments. In the process, this rivalry exhibited levels of intensity rarely seen today.

• Royals-Yankees AL Division Series Game 1 FAQ (Sat., 6:30 ET/5:30 CT, TBS)

Or maybe “intensity” is putting it too lightly.

"Hatred is probably the key word," Hall of Famer George Brett said Wednesday. "... Some older fans will remember. They’ll be telling their grandkids, saying, 'You should have seen these two teams play in the ‘70s -- oh my god. This was bad. These guys really didn’t like each other.' We really didn’t."

Before the Royals and Yankees clash on Saturday for ALDS Game 1, here is a primer on their shared past in the postseason and beyond.

• Royals-Yankees position-by-position breakdown

1976

An expansion team in 1969, the Royals reached the playoffs for the first time in ‘76. Meanwhile, the historic Yankees finally returned to the postseason after an 11-year drought, their longest since the club became known as the Yankees in 1913.

This David-versus-Goliath matchup went to a winner-take-all ALCS Game 5 at Yankee Stadium. With New York just six outs away from advancing to the World Series, Kansas City rallied in the eighth and tied the game on a majestic three-run homer from a 23-year-old Brett, who won his first of three batting titles that season.

The Bronx fell silent. But it wouldn’t stay that way for long.

The crowd whipped itself into a frenzy heading into the bottom of the ninth inning. The game was delayed momentarily as umpires and the grounds crew picked up objects that fans had thrown onto the field.

"That made it a little more anxious because it was cold," Yankees first baseman Chris Chambliss said. "We wanted to get going."

True to his word, Chambliss led off the inning and slugged the first pitch he saw from Royals right-hander Mark Littell over the wall in right-center for a series-clinching home run. Chambliss’ walk-off was more of a sprint as he was mobbed by fans while making his way around the bases.

And Chambliss wasn’t the only player who got caught up in the craziness. As Yankees outfielder Roy White dashed out of the dugout and toward home plate to congratulate Chambliss, he was hoisted up by the crowd

"It was a really uncomfortable feeling to be six feet high up in the air," White said with a laugh. "These people got you up, lifting you, twirling you around almost.

"It was like life or death to get back into the clubhouse. But that was just a great win."

1977

According to Brett, this rivalry really started in ‘77.

"To have a rivalry like that with a team outside your division, that says something," he said. "That tells you how big of a rivalry it was."

As the 100-win teams faced off once again in the ALCS, familiarity bred a lot of contemptuous baseball. It began in the sixth inning of Game 2 as the Royals’ Hal McRae broke up a possible double-play grounder by barrelling into Yankees second baseman Willie Randolph, sending the two players flying well past the bag.

McRae’s slide allowed Freddie Patek to come around from second base with the tying run. Randolph and the Yankees, however, got the last laugh in a 6-2 victory.

During Game 4 in Kansas City, Yankees third baseman Graig Nettles sought out some retribution and charged through Royals second baseman Frank White to break up a double play in another New York win.

All this bubbling tension boiled over in the first inning of another winner-take-all Game 5. Brett sent a ball to deep center and raced to third for an RBI triple. As Brett slid into the bag, he shoved back Nettles.

“Brett decided to slide in hard to third base to show that he was a tough guy,” Nettles said. “But he really wasn't.”

Nettles retaliated by kicking Brett in the mouth. The Royals star got to his feet and unleashed a haymaker.

"I just got up and popped him," Brett said.

The fight was on. The benches cleared quickly. No one was ejected.

"That would not happen today," Brett added. "Players are too close. The game is different.”

Order was soon restored, and the Royals held a 3-2 lead heading to the ninth. But the Yankees landed a knockout blow by scoring three runs in the inning to win the pennant.

1978

While the ‘78 ALCS didn’t have as much open animosity, it did contain a spectacular performance by Brett, who bashed three solo homers in Game 3 at Yankee Stadium and went 7-for-17 in the series.

But it was Yankees catcher Thurman Munson, playing with a badly injured shoulder, who provided the most important home run in Game 3: a two-run, go-ahead clout in the bottom of the eighth that propelled New York to a 6-5 win.

Roy White had a good view of Munson’s game-changing blast as he watched from first base after singling ahead of the Yankees’ captain.

"I was thinking it was just extra bases, that I was going to score," Roy White said. "It just kept going and going and the next thing you know, it was out."

The next day, Ron Guidry, the AL Cy Young Award winner in ‘78, outdueled Dennis Leonard in Game 4 as the Yankees triumphed, 2-1, and eliminated Kansas City for the third year in a row.

“Every game with them was like a war that we'd have with those guys for three straight years,” Roy White said.

1980

After both teams missed the playoffs in 1979, they were right back at it in ‘80. Nettles provided one of the few Yankees highlights of that ALCS with an inside-the-park homer in the fifth inning of Game 2. Nettles had recently returned to action after missing more than two months with hepatitis. His doctors told him he could do almost everything on the diamond -- field, throw, hit -- but to not do any running.

"So the first game back, I hit an inside-the-park home run. I thought I was going to die," he said.

Yet the Royals won that game, 3-2, and snatched the pinstriped monkey off their backs in emphatic fashion, sweeping the Yankees in three games and limiting their offense to only six runs.

Brett, that season's AL MVP, delivered the decisive swing in the seventh inning of Game 3 when he launched a pitch from dominant Yankees reliever Goose Gossage into Yankee Stadium’s upper deck for a go-ahead three-run shot.

"I knew Goose was going to throw something hard," Brett recalled. "He had a big ego. I had a big ego. I just said, 'Hey, don’t try to hit a home run. Just try to hit it hard. Be quick. Hit it hard and be quick.' And it was one of the farthest balls I ever hit, and probably the most meaningful swing in my career."

Yankees manager Dick Howser was fired after the season despite leading the club to a 103-59 record. He would become Kansas City’s manager during the 1981 season and helmed the franchise’s first World Series winner in 1985.

1983

Although 1980 would be the last Royals-Yankees postseason matchup until this weekend, we would be remiss if we didn’t mention one other intense encounter involving these two teams.

It is known simply as The Pine Tar Game.

It was July 24, 1983, and the Yankees were one out away from beating the Royals in the Bronx. Gossage was brought out of the ‘pen to hold onto a one-run lead with a runner on first. And up to the plate stepped Brett.

Just as he did in 1980, Brett got the best of Gossage, driving a pitch into the right-field seats to give the Royals the lead.

But Yankees manager Billy Martin wanted a word with home-plate umpire Tim McClelland. According to Martin, the pine tar on Brett’s bat extended past the 18-inch limit from its bottom. McClelland used home plate, which is 17 inches in width, to measure and ultimately ruled that, yes, the pine tar was too far up the bat.

After a short discussion, McClelland walked toward Kansas City's dugout, pointed at Brett with the bat in question and signaled that he was out.

And Brett went ballistic.

The Royals filed a protest to the league office and 26 days later -- after rulings from AL President Lee MacPhail and multiple court judges -- Brett’s homer was officially upheld, and the game resumed in the top of the ninth on Aug. 18.

The resumption lasted only 10 minutes as Royals closer Dan Quisenberry shut down the Yankees in the bottom of the inning. The Royals had prevailed at long last.

"I just did an interview with the Hall of Fame remembering the Pine Tar Game from both sides," Brett said. "Goose and I have become good friends, but I don’t know how many times he said in the 15-minute conversation we had with the writer how much he hated my guts and that he wanted to kill me. That was the rivalry."

Both franchises have experienced their ups and downs since '83. While the Royals were a winning club for most of the ‘80s, the Yankees didn’t make the playoffs between 1982-94. The Yanks then built a dynasty around the turn of the century while the Royals floundered near the bottom of the AL Central. The Yankees reigned again in 2009, and the Royals captured their second World Series title in 2015.

Household names such as Brett and Reggie Jackson have been replaced by Bobby Witt Jr. and Aaron Judge. Neither of those modern-day stars was born when the Royals-Yankees rivalry was at its apex. But now they have an opportunity to write a postseason story all their own.

Roy White said he will be in attendance for Game 1. Brett, the Royals’ vice president of baseball operations for more than three decades, will be there as well.

"It’ll be great. I’ll absolutely love it," he said.

MLB.com national reporter Bill Ladson and Royals beat reporter Anne Rogers contributed to this story.