SEATTLE — The Seattle Mariners entered Wednesday on a decent wave of momentum.

The Mariners had a four-game win streak and clinched their second consecutive series with a 5-3 win against the St. Louis Cardinals on Tuesday. Before the series finale against the Cardinals, the Texas Rangers beat the Milwaukee Brewers 6-3 to pull within one game of Seattle for the final American League wild card spot.

Seattle was within one game of the Houston Astros for first place in the AL West entering Wednesday.

With the AL playoff picture so closely-contested, Wednesday's series finale between the Mariners and St. Louis could prove to be a critical contest for the former. And a rookie infielder will be in the starting lineup after several days on the bench.

Cole Young will hit ninth and play second base for Seattle, according to the lineup posted by the team on "X."

Young, a former top 100 prospect, made his major league debut May 31 and has been the team's primary second baseman for the better part of the season since. He's scored 24 runs in 71  games and has hit seven doubles, a triple and four home runs with 24 RBIs. He's slashed .219/.311/.319 with a .630 OPS.

The first-year infielder has struggled over the last month. In August, he slashed .179/.343/.268. He's gone without a hit in 13 of his last 15 games.

Due to these struggles, Young has received less starts at second base over the last week. The team has to start Leo Rivas against right-handed pitchers and Jorge Polanco against lefties in that stretch.

"A chance to get (Young) in there off the right-hander tonight," Mariners manager Dan Wilson said in a pregame interview Wednesday. "Get some at-bats. What we've seen defensively has been outstanding. (Today's) a chance to get his swing back, get his feel back a little bit at the plate. Just looking for those good at-bats and making some solid contact, swinging at good pitches and driving the ball through the middle like he does. Cole has had an outstanding season and good to have him back in the lineup today."

If Young can get back to a consistent form ahead of the playoffs, Seattle will have several solid options in the middle infield for the final stretch of the season and the postseason. If not, the Mariners will likely continue to rely on Rivas and Polanco at second base.