CHICAGO -- Not long after Kris Bryant sent a pitch over Wrigley Field's center-field wall, where the ivy clinging to the bricks is beginning to blossom in patches, the chant swept through the stands. The grand slam shook the beams around the ballpark and the panic of early April seemed a distant memory.

"SWEEP! SWEEP! SWEEP!"

Bryant's eighth-inning slam on Sunday night was the exclamation point on a 13-5 rout of the rival Cardinals, giving the Cubs seven straight wins and completing a three-game brooming of the Redbirds to claim first place in the National League Central. That Chicago sits atop the division right now is remarkable, considering how brutal the team's results were over the first two weeks of this season.

• Box score

In the span of 30 days, the Cubs have climbed out of the NL Central cellar and into first, rattling off an MLB-best 18-6 record since a 1-6 start to the season. Yes, that first week was a very small sample, but the extent to which Chicago's pitching struggled had alarms ringing among much of the fan base. Manager Joe Maddon set a goal of gaining back one game per week, and his club did even better, turning a 5 1/2-game deficit into a half-game lead in a month's time.

"You normally don't have this quick rebound under these circumstances," Maddon said. "Nobody in that room believed we were going to maintain that negative approach. We just don't do that."

Sunday's victory served as a microcosm for how the Cubs turned things around.

Rotation set the tone

Left-hander José Quintana cruised through five shutout innings before finally flinching in the sixth inning. His outing gave the Cubs' lineup time to get something going against long-time Cardinals pitcher Adam Wainwright, and followed a recent trend for the North Siders.

The Cubs have received a 2.49 ERA from its rotation over the past 20 games after the group had an uncharacteristic 6.52 ERA over the first 11 contests this season.

"It starts with the starting pitching,” Maddon said. “The starting pitching has been good, and that's permitted us to get on this role."

Quintana, specifically, has stepped up in a big way for the Cubs. Over his past five starts, the lefty has gone 4-0 with a 1.93 ERA in 32 2/3 innings. Chicago also won the lone outing in that stretch that ended in a no-decision. Quintana surrendered a two-run double Yadier Molina in the sixth inning, but that was as far as St. Louis got against the southpaw.

"It was important for us to take first place right now and keep going like we've been playing," Quintana said. "That's a really good feeling. We know we played a really good team. They play in the same division, so it was important to win that game."

Lineup keeps thriving

During the first seven games of the season, the Cubs reached double-digits in runs three times and lost two of those games. The offense has been production since Opening Day, but it took time for the starters to find rhythm and for the bullpen to establish roles.

At the same time, players like Willson Contreras (1.110 OPS), Jason Heyward (.914 OPS) and David Bote (.861) have helped buy some key hitters like Bryant time to find their footing. In Sunday's win, Contreras was at it again, belting his ninth homer of the season and adding an RBI single. Heyward tripled and scored. Bote contributed an RBI double and a sacrifice fly.

"They've done a wonderful job," Maddon said. "There's a lot of chicken left on the bone, man. There's a lot more to do here, and these guys are definitely pointing in the right direction."

Javier Báez has been playing at an MVP-caliber level all season, and Anthony Rizzo has turned things up a notch over the past couple of weeks as well. Bryant -- mired in a slump for most of April -- has reached base in 15 straight games and has been making hard contact more consistently.

In the eighth, when Cardinals reliever Dominic Leone was laboring to harness his command, Bryant was hoping to get one more swing in.

"I really wanted that at-bat," Bryant said. "Some people don't want that last at-bat, sometimes, when you're not going great. But I feel great. I really wanted it. I'm seeing the ball good. I got it in the air. It was just good. It felt really good to see results after all the hard work that I've been putting in."

Bullpen doing its part

The two home runs launched by the Cardinals in the ninth inning masked an otherwise productive night for the Cubs' relief corps. Those blasts also came with Tyler Chatwood pounding the strike zone in a rout. The right-hander began with an 11-run cushion, so he was not going to nibble.

"I'll take that," Maddon said.

Brandon Kintzler took over for Quintana in the seventh and logged one shutout inning. Steve Cishek followed suit in the eighth. Those two have been a part of the bullpen cast that -- like the rotation -- has moved far beyond the woes of the first two weeks.

Over the past 22 games, Chicago's relievers have combined for a 2.11 ERA in 76 2/3 innings. That comes after the 'pen had an 9.51 ERA prior to that stretch.

"They've been way more consistent in the strike zone," Contreras said. "Everything is a process. I'm proud of my pitching staff overall -- the starting and relievers. They're being so good for this team. That's a huge help for us."