A's fans might have forgotten about Frankie Montas as he went through his struggles over the past month. Allow Montas to reintroduce himself.

After pitching himself out of contention to start in the A’s upcoming Wild Card Series -- which begins Tuesday against the No. 7 seed White Sox -- Montas was spectacular in Sunday’s 6-2 victory over the Mariners at the Coliseum, reminding why he was considered their ace entering 2020. The right-hander struck out a career-high 13 and allowed two unearned runs over six innings.

• Box score

The win helped Oakland lock up the No. 2 seed in the American League, setting up a matchup with the No. 7 seed White Sox in a best-of-three series. Chicago will start Lucas Giolito in Game 1, and Oakland will hold off until Monday to announce its starting pitching plans.

• 16-team postseason field set

Montas -- Oakland’s Opening Day starter -- entered Sunday with a 10.88 ERA over his previous six starts. Quite possibly pitching with a postseason roster spot on the line, he likely at least sealed a role out of the bullpen after limiting Seattle to four hits, all singles, and two walks.

“He pitched with an edge today,” A’s manager Bob Melvin said. “I was going to take him out after five, but I really needed him one more inning. He came in before I said anything and said, ‘I want one more’ and then struck everybody out. I think that’s going to do wonders for him going forward.”

Of Montas' 13 strikeouts, 10 were swinging. Montas also diversified his putaway options, recording six on his fastball, five on his slider and another pair on his sinker and splitter. Usually reliant on his heater, Montas actually used his slider the most against Seattle, throwing it for 35 of his 113 pitches while generating eight whiffs.

Montas’ propensity for punchouts on Sunday reached historic levels. His 13 strikeouts were the most by an A’s pitcher since Todd Stottlemyre struck out 15 in a 10-inning start against the Royals on June 16, 1995.

So what changed for Montas?

“It looked to me like after the first couple of innings he just got upset and said, 'The heck with it,'” Melvin said. “A lot of times, you get caught up in mechanics and pitch selection, and there’s a lot of clutter. He just pitched with some anger, I think. From the third inning on, it was dominant.”

The thought of Montas in the A’s bullpen could be a scary one for postseason opposition. The righty maxed out his fastball at 98.2 mph on Sunday, and that velocity would likely increase pitching in shorter bursts.

“Whatever I have to do to help the team win, I’m down for it,” Montas said of his postseason role. “Starter or reliever, whatever they want me to do, I’ll do it.”

The hot topic surrounding the A’s over the past week has been their lack of offensive production. One game doesn’t necessarily cure those woes, but the A’s offense will enter the postseason with some positive momentum, with a few hitters swinging the bat well, including Mark Canha, who drove in four runs on Sunday, and Jake Lamb, who launched a go-ahead solo home run in the seventh.

Chad Pinder, who was reinstated from the 10-day injured list prior to the game, entered in the third as a pinch-hitter and went 1-for-3 with a game-tying RBI single in the fifth.

“Any feeling of confidence can blossom into something really good,” Pinder said. “Ending the season with a win like that, tied through seven innings and you get a big home run, those are things people may look back on as the energy you need going forward. Hopefully we can continue that positivity going into this three-game series.”