ST. PETERSBURG -- Ryan Yarbrough establishing himself as a reliable option in the rotation is one of the reasons the Rays are in contention for one of the two American League Wild Card spots.

But as successful as Yarbrough has been this season, especially in the second half, his last two starts haven’t been too kind for the left-hander. After allowing six runs over five innings in his previous start, against the Angels, Yarbrough struggled again on Sunday, allowing six runs over 3 1/3 innings as the Rays lost to the Red Sox, 7-4, at Tropicana Field.

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“Just really frustrating today,” Yarbrough said. “Take a look at it tonight, think about some things and get back at it tomorrow.”

With the loss, the Rays ended Sunday in a tie with the Indians for the second AL Wild Card with six games left in the regular season. Both clubs were two games back of the A's for the top Wild Card.

The Red Sox offense attacked Yarbrough right out of the gate. Boston collected six hits in the first inning, with Christian Vázquez's three-run home run serving as the biggest blow.

Despite the four-run first inning for the Red Sox the Rays answered right back, scoring one run in each of the first three frames to cut the deficit to 4-3. Unfortunately for the Rays, they were unable to complete another comeback as the Boston offense continued its attack throughout the game.

Yarbrough ran into more trouble in the fourth inning after allowing a one-out double to Jackie Bradley Jr. and walking Rafael Devers. That ended his outing, which was the shortest since he became a set starter on Aug. 11. Over his last two starts, Yarbrough has allowed 12 runs over 8 1/3 innings. It was also the first time Yarbrough has lost back-to-back decisions in his career.

“I think that’s what makes it that much more frustrating right now. I know how good I can be,” Yarbrough said. “Things just aren’t going my way right now. Understand that that’s baseball and it’s not going to be all going your way all year. At this time of the year, it shouldn’t be happening, especially where we’re at right now in the race.”

Yarbrough has one start remaining in the regular season and the Rays are going to rely on the left-hander to bounce back with the team in the thick of a playoff race. A positive for Yarbrough was that he threw 40 of his 63 pitches for strikes, but he struggled to put hitters away once he got ahead in the count. Yarbrough doesn’t believe the problem is mechanical, but will sit with pitching coach Kyle Snyder to figure out what the right approach is before his next start against Toronto.

“It looked like early on he couldn’t execute pitches when he got ahead,” said Rays manager Kevin Cash. “He got ahead of guys, he just couldn’t put them away. They had good at-bats against him.”

Andrew Kittredge relieved Yarbrough but struggled with his command. Kittredge hit Xander Bogaerts and walked J.D. Martinez with the bases loaded to give the Red Sox another run. In the next at-bat, Kittredge pulled an 0-2 slider away from catcher Mike Zunino that resulted in a wild pitch and allowed Devers to score to make it 6-3.

Uncharacteristically, the Rays defense also struggled on Sunday. The club committed two errors, in addition to a couple of other plays that the defense has made consistently over the course of the season.

That, combined with the offense going quiet over the final six innings with the exception of No. 2 Rays prospect (according to MLB Pipeline) Brendan McKay’s first career home run in the 9th, ultimately ended the comeback bid for the Rays.

“We’re going to lose at some point,” said Rays infielder Joey Wendle, who homered on Sunday. “It’s disappointing. You never want to lose when you’re in a race like this, but it’s a pretty good team over there. We’ll hopefully come back out tomorrow and get a series win.”