CLEVELAND — The most important series of the season is here, fittingly in mid-September, as the Twins have a chance to put themselves in much better position in the American League Central race.

Trailing the first-place Guardians by four games, the Twins begin a five-game series at Progressive Field by starting Bailey Ober, who completed a rehab assignment from a groin injury and was activated.

His opponent tonight (6:10 p.m., BSN) will be Cleveland's Tristan McKenzie (10-11, 3.05 ERA), who beat the Twins on Saturday at Target Field.

Ober was 1-2 with a 4.01 ERA before his injury. To make room for Ober on the 28-man active roster and the 40-man roster, reliever Jharel Cotton was designated for release or assignment, as he had been earlier this season. If he clears waivers, he'll go to St. Paul.

The Twins also placed Kyle Garlick (left wrist sprain) on the 10-day injured list and recalled outfielder Mark Contreras from St. Paul. Contreras will start in right field tonight.

And pitcher Randy Dobnak, out all season because of a finger injury, cleared waivers and was assigned to the Saints.

Jorge Polanco (knee) and Trevor Larnach (core muscle surgery) are on rehab assignments in St. Paul. Matt Wallner has been called up from the Saints to be on the taxi squad.

Louie Varland will be the 29th man tomorrow and start Game 1 against former Cy Young winner Shane Bieber.

The series runs through Monday, with a doubleheader tomorrow. The teams are making up two postponed games from the first week of the season, which was delayed by the lockout.

Luis Arraez, battling a hamstring injury, leads the AL in batting and will lead off tonight for the Twins.

TWINS LINEUP

Luis Arraez, DH

Carlos Correa, SS

Jose Miranda, 1B

Nick Gordon, 2B

Gio Urshela, 3B

Gary Sanchez, C

Jake Cave, LF

Gilberto Celestino, CF

Mark Contreras, RF

GUARDIANS LINEUP

Steven Kwan, LF

Amed Rosario, SS

Jose Ramirez, 3B

Josh Naylor, 1B

Oscar Gonzalez, RF

Andres Gimenez, 2B

Will Benson, DH

Luke Maile, C

Myles Straw, CF