With the No. 1 seed in the Wild Card Series secured, the Dodgers went back to the lab on Wednesday to prepare Julio Urías for postseason bullpen duty, scratching the lefty hours before his announced start and replacing him with opener Joe Kelly.

The swap of roles, announced hours before the Dodgers lost to the A’s, 6-4, was to test Urías as a long or “bulk” reliever, and it went well. He entered in the third inning, skipping past the first inning that has caused him so much trouble this year, and allowed one run in six innings with five strikeouts.

“I thought this was one of his best outings,” manager Dave Roberts said of Urías. “I just love the way Julio has embraced whatever we ask of him. He’s all in.”

Roberts has previously called on starters Dustin May and Tony Gonsolin to pitch bulk innings of relief, apparently preparing for unconventional postseason tactics. On Wednesday, he said Clayton Kershaw and Walker Buehler would pitch the first two games of the best-of-three Wild Card Series (the order undecided), but a Game 3 starter is still to be decided.

Roberts said he might move Gonsolin into the bullpen in similar fashion instead of what had figured to be his last regular-season start on Saturday. May is scheduled to pitch on Sunday.

Urías has a 3.75 ERA in 11 postseason relief appearances, but he’s been a starter this year.

• Gear up for October

Buehler, one of the biggest question marks for the postseason, is expected to come off the injured list and start on Thursday. He has been limited to 7 2/3 innings since Aug. 21 because of two stints on the sidelines with a right index finger blister. If he starts Game 2 of the Wild Card Series, he would have a full week off for the finger to recover.

Kelly, committed to throwing mostly breaking balls on back-to-back nights, allowed the first three Oakland batters to reach base and score, one of the runs unearned on a Cody Bellinger throwing error that skipped past third baseman Justin Turner.

“I do think as we look out, a little changing of the mix and adding fastballs to keep those guys honest makes some sense,” Roberts said of Kelly. “[The curveball is] an elite pitch when it’s right, but when a Major League hitter knows it’s coming, the margin gets a little bit smaller.”