Mark Prior has no answers for the inconsistency that has plagued him this season, and Dusty Baker isn't sure what's ailing Prior either.

But after Prior suffered through a rough outing in an 8-6 loss to San Diego, the questions are sure to continue.

Prior allowed six runs on eight hits in three innings, tying a career high with five walks and hitting a batter. He has yet to win back-to-back starts, has yet to win at home and is 3-3 with a 4.89 earned-run average in 12 starts since returning from Achilles' tendinitis and elbow problems June 4.

Prior was at a loss when asked about his lack of control.

"I don't know," he said. "Do you know? I've never really had that much problem in games. I've had probably my fair share of more games where I've struggled with control than I have in years past. But I don't have one specific answer."

It's a marked contrast from last year, when Prior won 10 of his last 11 starts.

"It's a new year," Baker said. "You can't keep talking about last year. We've got to figure out how to stay out of those stretches this year. That's what [pitching coach Larry Rothschild] and him are doing. They go to the video room, go to the drawing board ... he'll find it. This guy can pitch."

San Diego catcher Ramon Hernandez homered and drove in four runs as the Padres took the opener of the three-game series, moving to within one game of the Cubs in the National League wild-card race.

Sammy Sosa hit his 564th career home run to pass Reggie Jackson for eighth place on the all-time home run list, a solo shot off Padres starter Adam Eaton in the second. Derrek Lee added two solo homers and Moises Alou and Nomar Garciaparra also hit solos, but Prior's wild streak and a defensive lapse by Glendon Rusch made the home run barrage a moot point.

"I'll take five solo homers any day," Lee said. "Most of the time with our pitching staff, five solo homers is going to be enough to get us the win."

Not this time.

Back-to-back homers by Sosa and Alou in the second staked Prior to a 2-0 lead before he fell apart in the third. After starting a double play that left a runner on third with two outs, Prior thought he'd struck out Ryan Klesko with a picture-perfect curve that froze the Padres slugger. But plate umpire Bruce Froemming called it a ball, sending Klesko to first with a walk.

"I don't know if [Froemming] was being hard on him or not," Baker said. "But that was a big pitch."

At that point Prior became completely unglued. Terrence Long singled home the first run, and Hernandez tied it up with another RBI single. After walking Khalil Greene to load the bases, Prior served up a two-run single to Eaton, a .163 hitter.

After Mark Loretta singled leading off the fourth, Brian Giles doubled and Prior plunked Phil Nevin to load the bases and force his exit. The three-inning start was Prior's second shortest, following a 12/3 inning outing July 15 when he complained of elbow soreness. After missing one start with what he called a "freak" injury, Prior has had two strong outings and two poor ones.

Rushed into action, Rusch did himself no favor by failing to cover first on Klesko's grounder between first and second, allowing another run to score. After a double play Rusch gave up a three-run homer to Hernandez, making it 8-2. Three more homers, including Lee's second in the ninth, pulled the Cubs to within two. But closer Trevor Hoffman induced Ramon Martinez to fly out to end it with the tying runs on.