Not even the return of Chris Bassitt was enough to spark the Oakland Athletics.

Bassitt made his first appearance Thursday since taking a 100 mph liner to the face Aug. 17.

The right-hander pitched three scoreless innings and left with a three-run lead, but the A's couldn't hang on and lost 6-5 to the visiting Seattle Mariners, who swept the four-game series.

It won't get any easier for the A's, as the American League West-leading Houston Astros come to town for a three-game series starting Friday.

Oakland (82-71) is now four games back in the chase for the AL's second and final wild-card playoff berth, with nine games left.

"We are so far behind the 8-ball right now in the standings that it's tough to look at," Bassitt said. "Obviously, the last month has been terrible for us."

Bassitt was leading the league with 12 wins and the A's were in playoff position when he was hit by a ball struck by the Chicago White Sox's Brian Goodwin. Bassitt needed stitches and required surgery to repair a fractured cheekbone.

Oakland went 14-18 in his absence, dropping out of playoff position.

"It is what it is," Bassitt said. "We haven't done a good enough job to win games. But I'm still happy as hell to be a part of this group."

The A's totaled just 10 runs in the four games against Seattle, with half of those coming via solo homers.

"Very disappointing," Oakland manager Bob Melvin said. "Four-game sweeps are tough to do. We're at home and we have a lot to play for. They got big hits when they had to. (The Mariners are a) a team that doesn't score a ton of runs. You'd think when you score five, you have a chance to win this game."

The Astros (91-62) still have something to play for, as they are three games behind the Tampa Bay Rays (94-59) for the league's best record.

Houston had a four-game winning streak snapped with a 3-2 loss Thursday night against the Los Angeles Angels in Anaheim, Calif.

The Astros' magic number for clinching the division title remained at three following the defeat that was charged to Lance McCullers Jr. The right-hander gave up three runs on two hits in six innings, getting hurt by issuing four walks.

Manager Dusty Baker said of McCullers, "He's amongst the league leaders in ERA and one of the toughest to hit in the league. The only thing that's plagued him has been some untimely walks, but this guy, he's thrown the ball well all year."

Astros right-hander Zack Greinke (11-6, 4.11 ERA) is scheduled to start Friday. Greinke is 11-3 with a 2.66 ERA in 23 career appearances against Oakland, including 19 starts. He is 2-0 vs. the A's this season, winning a pair of starts by 8-1 scores. In 14 innings, he has allowed one run on seven hits, with no walks and 12 strikeouts.

In his past three outings, Greinke has failed to go longer than five innings or allow fewer than five earned runs -- and those starts came against the cellar-dwelling Texas Rangers (twice) and Arizona Diamondbacks.

The A's plan to counter with right-hander Frankie Montas (12-9, 3.57 ERA). Montas is 6-4 with a 3.75 ERA in 12 career appearances against Houston, with 10 starts. He is 2-1 vs. the Astros this season, having allowed just four runs on 18 hits in 17 2/3 innings, with four walks and 21 strikeouts.

In his latest outing, Sunday against the host Angels, Montas pitched seven shutout innings of one-hit ball in a game Oakland won 3-2 in 10 innings.