BOSTON -- Entering the day with the slimmest of leads over the Tigers for the third American League Wild Card spot, the Twins had reason for optimism going into the first game of Sunday’s split doubleheader against the Red Sox.

Minnesota had staff ace Pablo López going on the mound in his first career appearance at Fenway Park. López easily handled the Red Sox earlier this season at Target Field, allowing just one run in six innings with eight strikeouts on May 4.

But any optimism was quickly dashed when Boston first baseman Tristan Casas bashed the first of his three home runs, with two outs and two runners on base in the first inning, and the Twins dropped an 8-1 decision. Minnesota (81-74) fell a half-game back of Detroit (82-74), which beat Baltimore, and Kansas City (82-74), which lost to San Francisco, in the Wild Card chase.

“There’s no sugar-coating it,” López said. “Not the performance I was looking for, especially with what this game means. Game 1 of a doubleheader, didn’t provide the length, didn’t provide the quality. And we know what this game also meant with playoff implications.

“So, all in all, not an easy game. Didn’t do my part. I put the team in a hole very quickly with a three-run lead, and then even deeper with the other four runs that I allowed.”

Casas repeated his earlier homer feat in the third inning with another three-run blast off López and added a solo homer in fifth off left-hander Brent Headrick, who made his first MLB appearance of the season after being called up from Triple-A on Saturday. It was Casas’ first career three-homer game.

In 11 previous starts since the All-Star break, López had gone 7-1 with a 2.01 ERA. The most runs he had allowed in a start in that span was four to the Cubs on Aug. 6. López’s next win would make him the Twins’ first 16-game winner since Ervin Santana in 2017.

López took the loss, falling to 15-9 as his ERA jumped from 3.84 to 4.11. He lasted just four innings, matching his shortest outing of the season, and tied a season high with seven runs allowed on nine hits, one walk and three strikeouts. The two homers allowed also matched a season high.

“So, not the performance I wanted to give the team,” López said. “Very frustrating, very disappointing, too, for the team, the fans. But we get to play another game [tonight]. I know the clubhouse right now is looking to the next one. That’s my mentality, too.”

The loss also snapped López’s string of five consecutive winning decisions after going 5-0 in his seven previous starts. In that span, he allowed just seven total runs and two homers in 46 2/3 innings, with no earned runs allowed in four of those outings.