A middle reliever and occasional starter since reaching the big leagues in 2004 with the Mariners, Baek has been thrust into the rotation with the Padres this season because of injuries that have sidelined starters Chris Young and Shawn Estes.
And the progress has mostly been forward since Baek came over from Seattle on May 28 in exchange for right-hander Jared Wells. Baek won his first outing for the Padres, and in his previous two starts, the right-hander had allowed just four runs in 13 innings.
But the numbers turned against Baek, who pitched into the seventh inning for the second straight start and paid for it, as the Padres dropped a 7-5 decision Saturday night to even their Interleague series against the Tigers at a game apiece.
Delivering the big blow for Detroit was Marcus Thames, who broke a tie in the top of the seventh with a two-run shot to the deepest part of the ballpark in left center.
The Tigers improved to 11-1 this season when Thames homers and 50-19 when he homers in his five seasons with the club.
Baek had benefited from a pair of rallies, the second of which gave him a lead that he carried into the seventh. But Clete Thomas, who struck out on three pitches in his previous at-bat, doubled to lead off the inning and went to third on Brandon Inge's sacrifice that was nearly bobbled, as Baek and Michael Barrett collided before Barrett threw out Inge.
Jeff Larish then delivered a pinch-hit chopper up the middle past a drawn-in infield to score Thomas to tie the game.
"I guess that is how you define tough," manager Bud Black said of the inning. "A leadoff double, a bunt and a couple-hopper up the middle that found the hole. He got ahead of him 0-2, and Larish bounced one."
Coming over from the American League, Baek was familiar with the Tigers and last faced them May 21, when he pitched three scoreless innings in relief.
Baek (1-2) relied heavily on his slider Saturday and threw changeups in off counts, but he took the loss after allowing six runs on eight hits over 6 1/3 innings. He also tied a career high with seven strikeouts.
"He did a pretty good job today to keep us in the ballgame," Barrett said. "They capitalized on a few mistakes early and got ahead late in the game to put the pressure on us, and their guys in the 'pen shut us down."
Baek was lifted for left-hander Justin Hampson after Larish's single, but Tigers manager Jim Leyland countered with Thames, who elevated a high changeup. That made a winner out of Nate Robertson (6-6), who allowed five runs on seven hits and two walks with five strikeouts.
"Thames is hitting below .200 against lefties, and if Justin executes his pitches down, he gets him," Black said of Thames, who was hitting .188 against left-handed pitching. "That is where you have to attack Thames."
The game featured four lead changes and opened quickly as Curtis Granderson demonstrated the value of speed at PETCO Park.
In his first two at-bats, Granderson reached third base and was driven home on sacrifice flies. He led off the game with a double into the right-field corner, went to third on a passed ball and scored on Carlos Guillen's sac fly.
In the third, Granderson hit a 75-foot infield single that Chase Headley fielded and threw away for a two-base error. Granderson then trotted home on a sac fly by Placido Polanco.
Barrett handed the Padres their first lead of the game with a two-run shot in the bottom of the second. Headley led off the inning with a broken-bat single that landed in no-man's land in shallow right and scored on Khalil Greene's triple to the fence in right-center.
Barrett went to a 2-2 count against Robertson before hammering a pitch into the left-field seats for his second homer of the year and a 3-1 Padres lead. Prior to the game, Barrett worked with hitting coach Wally Joyner to help end a 6-for-44 slump entering Saturday.
"We got together today for early BP and talked about a lot of things and made quite a few adjustments that helped me," Barrett said. "I just tried to stay concentrating on what we worked on today and eliminate the pitch selection. He made a good pitch, and I just put the bat on the ball and good things can happen."
Granderson gave some runs back, as he misplayed Edgar Gonzalez's fly ball in fifth. The Padres' second baseman hit a drive to the right-center gap, which Granderson misread. He paused and hesitated before sprinting back to his left.
That momentary lapse produced a two-run double, as Scott Hairston and Jody Gerut scored to give the Padres a 5-4 lead.
Center field also presented challenges for Gerut, who nearly hauled in a drive by Magglio Ordonez in the third. The Tigers' right fielder hit a 1-0 pitch from Baek to dead center. Gerut went back and leaped at the wall, but the ball glanced off his glove and over for a two-run homer, Ordonez's 11th of the year.
"It bounced. If you give me 1,000 tries [on that play] I don't think I could do that again," Gerut said. "Tough bounce. I thought it was in the ballpark."
Mike Scarr is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.