The Marlins let a five-run first inning lead disappear, and they were unable to protect a one-run margin in the ninth. Still, they prevailed in an endurance test at Petco Park.
Hanley Ramirez walked to open the 12th and scored from first on Infante's double to the wall in left-center.
The nine runs matched the Marlins' season high, previously set in a 9-1 win over the Cubs on April 18. Steve Cishek threw three scoreless innings to secure Miami's fourth straight win.
The Marlins' ability to rally and finally getting some run support were encouraging, but the night also was bewildering because starter Josh Johnson labored again and closer Heath Bell blew his fourth save in seven tries.
"Those types of games can carry over to the next game, because this kid [Cishek] stepped up," Guillen said. "He's been great all along."
The Padres forced extra innings by scoring the tying run off Bell, the former San Diego All-Star. Pinch-hitter Jesus Guzman opened the ninth with a double, and Cameron Maybin's RBI double to right knotted the game at 8. The Padres loaded the bases with two outs, but worked out of it when Chase Headley ripped a liner that second baseman Infante fielded on a short hop. Bell threw 33 pitches in the ninth, with 16 strikes.
Bell's problems have Guillen rethinking what to do about the closer situation.
"Bell continues to struggle," Guillen said. "We will recheck tomorrow what will be that situation, closing. We've got to do something about it. We can't be waiting any more. Then we'll figure out tomorrow. We might talk to him about it.
"If we want to be in the pennant race, we've got to be better."
With Cishek, a likely candidate to close, throwing three innings on Friday, he will not be available for a few more days. The 25-year-old also threw two innings on Wednesday at San Francisco.
Roster moves are expected before Saturday's game.
"I feel fine. I was even saying to somebody, if I was hurt, then I could actually explain my bad luck right now," Bell said. "It's just nothing is going for me right now. Every day I come in here, I'm positive. I feel like I can get the job done."
In their previous series, the Marlins managed to sweep the Giants in three games, scoring a total of eight runs. They stranded 15 on base in Thursday's 3-2 win. Afterward, Guillen said more offense was needed.
Miami responded in the first inning on Friday, posting a season-high five runs off Anthony Bass on Ramirez's three-run homer and a two-run shot by Giancarlo Stanton -- the first time the Marlins have hit two homers in an inning since the third on Sept. 9, 2011, against the Pirates.
The big lead didn't hold as the Padres rallied for six runs in the third off Johnson, who faced nine batters and didn't make it through the inning. The damage came with two outs when five straight Padres reached. The big blow was delivered by Bass, who was down two strikes in the count, before lining a bases-loaded triple to right.
Johnson threw 36 of his 67 pitches in the third.
"You're up, 5-0, and JJ is on the mound, you feel good about yourself," Guillen said. "I just wonder if he's not feeling good. He says he feels good, but command is not there. A lot of bad pitches. With two strikes, keeping the ball up. Right now, what's killing him is he doesn't have any command of his pitches."
Johnson, who missed most of last year with right shoulder inflammation, maintains he's healthy. Yet, he saw his ERA raise to 6.61, and he's allowed 47 hits in 31 1/3 innings.
"Physically, I feel good," he said. "When you throw the ball in the middle of the plate, it's going to get hit. If you look at all of them, right down the middle."
Normally even-keel, Johnson noted he was probably the most angry at himself ever since he's been in the big leagues.
"I'm wearing my bullpen out, which kills me, especially today," Johnson said. "We get the five runs early, and then just squander that lead like that. It's unacceptable."
The Marlins tied it at 6 in the fourth, courtesy of Jose Reyes creating havoc. Reyes doubled and reached third with two outs. With Reyes starting and stopping on the basepaths, Bass balked in the tying run.
"This was a huge comeback," Guillen said. "They take the lead and we could easily hit the tank, the way we had been hitting."