One week after watching the Seattle Mariners sabotage their chances of winning the American League West, the Oakland Athletics get a chance to return the favor when they visit the Mariners for a critical three-game series that begins Monday night.

Thanks in large part to a four-game sweep in Oakland at the beginning of last week, the Mariners (86-70) have overtaken the A's (85-71) in their duel for second place in the AL West and, more important, their pursuit of an AL wild-card spot.

The chances of the Mariners or the A's catching the West-leading Houston Astros (91-65) are remote. In fact, a Seattle win on Monday would formally eliminate the A's.

But both are very much alive in the wild-card chase, with Seattle beginning the week two games out of the second spot and Oakland three.

Suffice it to say, any loss in this series by either team could be disastrous.

The Mariners are hoping the three-game set begins like the third game of last week's series went down -- with Chris Flexen outpitching Cole Irvin. As it was in Seattle's 4-1 win five days ago, that's the scheduled matchup Monday.

Mariners manager Scott Servais said he wouldn't want it any other way.

"We would not be in this spot without the efforts (of several players) this year," he gushed over Flexen's performance last week, "but maybe none bigger than Flex."

Having attended high school in the shadow of Oakland's home field, Flexen (13-6, 3.56) has never lost in Oakland, going 2-0 with a 1.32 ERA.

A high school senior when the A's started a run of three straight postseason appearances in 2012 behind a staff that featured Bartolo Colon and another local product, Tyson Ross, the 27-year-old limited the A's to one run -- a Matt Chapman home run -- and three hits in seven innings with eight strikeouts in last week's homecoming.

He has gone 2-2 with a 3.24 ERA in four starts against the A's this season, the first four times he's faced them in his career.

Irvin (10-14, 3.99) will be seeing the Mariners for a fifth time this season. Last week's loss was his fourth straight against the AL West rival, having allowed 14 runs and 29 hits in 16 2/3 innings in those games.

Those were the only four times the left-hander has faced the Mariners in his career, compiling a 7.56 ERA to go with the 0-4 record. Irvin served up solo home runs to Kyle Seager and Ty France among seven hits in five innings in last week's loss.

The A's learned Sunday that Elvis Andrus, injured when scoring Oakland's winning run Saturday, had suffered a broken left leg. He will be lost for the season, as will second baseman Jed Lowrie with a sprained right hand.

When replacement shortstop Josh Harrison had to leave Sunday's game with a sore knee, little-used Vimael Machin was pressed into action and played a key role in a 4-3 win over Houston with two bunts -- a seventh-inning sacrifice that set up two runs and a ninth-inning hit that came three batters before Mark Canha's walk-off.

A's manager Bob Melvin was beaming about the bunts afterward.

"We're not opposed to it," he assured. "The tough part is when you bunt in those spots, it takes the bat out of (Matt Olson's) hands. But we feel confident enough in the other guys to get it done."