Riding the momentum of Sunday's Bedlam rally with a Big 12 Championship on the line in the weekend ahead, the Sooners stumbled on their Achilles' heel -- a midweek game.
Dallas Baptist (27-26) outlasted No. 18 Oklahoma (35-17) 6-4 at L. Dale Mitchell Park for the Sooners fourth straight loss on a Tuesday and their seventh in the last nine games overall.
The Patriots ripped a five-run third inning to take a lead and control a late Sooner rally.
"It's been real frustrating," OU shortstop Jack Mayfield, one of five Sooners honored on Senior Night, said. "We're just lacking little things, scoring those little runs. We gave up six runs today and gave up that home run at the end -- that really killed us."
Dallas Baptist gift-wrapped OU's early lead. With two outs, senior Max White reached on an error by third baseman Duncan McAlpine and rounded the corners after a Matt Oberste single and passed ball and finally scored on a wild pitch.
OU's trouble started in the third when a one-out base on balls issued to leadoff hitter Boomer Collins was followed by back-to-back two-out singles to load the bases. Leftfielder Austin Listi smacked Adam Choplick's (3-3) 2-1 fastball down the left field line for a base-clearing double.
"We pitched to them like they were Babe Ruth in the second and third innings," OU head coach Sunny Golloway said. "Once Choplick walked (Collins), I think he was afraid to walk anybody else and left balls down the middle."
Choplick walked Mike Weslowski on four pitches in the next at-bat before he was lifted in favor of reliever Kindle Ladd. The Patriots followed the move a single and double for back-to-back RBIs.
"This loss is big for us," Golloway said. "We've lost two to Arkansas-Little Rock, we've lost two to DBU and we've lost to UT-Arlington and we don't do that. We don't. That is not typical Oklahoma."
Oklahoma's loss to Dallas Baptist was its sixth consecutive, the second longest active losing streak the Sooners have against any opponent. The only longer is a seven-game losing streak to Arizona, a team Oklahoma has not faced since 1979.
"We played behind in all those games. That's not good for hitters."
Oklahoma managed just five hits in 33 at-bats.
Garrett Carey knocked Oklahoma's third base hit with a double to lead off the seventh and rode the basepaths following a groundout, hit by pitch and single to score OU's second run.
Following an errantly thrown double-play attempt by DBU in the eighth, freshman Kolbey Carpenter batted in Hector Lorenzana and Garrett Carey to close the game to 5-4.
Ladd managed a career-high six strikeouts in six innings of work, but was driven over left field on a first-pitch solo home run by Collins in the top of the ninth.
"That was a tough loss, a tough last home game," Mayfield said. "We've got to keep fighting. We've got to sweep, so we'll try to get that sweep at Kansas State."
The Sooners enter Friday's first of a three-game series two victories behind the Wildcats in the conference race.