Cunningham was making his first start, in right field, since being called up from Triple-A Portland on Friday after Matt Stairs went on the disabled list. Cunningham, who played parts of the last two seasons for Oakland, hit his slam to center field on an 0-1 changeup from Cecil with one out in the second.
"I would have been happy with a single or just getting on base, a walk or whatever I could do to help the team," he said. "It just turned out to be the best possible scenario."
It was his third career home run and the fourth slam by the Padres this season. The Padres loaded the bases on a double by Nick Hundley -- the first of his three hits -- a walk to Chris Denorfia and a single by Jerry Hairston Jr.
"I had the nerves going, the adrenaline going, and I just hit it," Cunningham said. "I almost passed Jerry going around second base."
Cecil knew Cunningham was out in front of the pitch. "I don't know how it got out," Cecil said. "He's got some strong wrists. It could have been a better pitch, but it was still a good pitch."
Cecil thought it would be a sacrifice fly that center fielder Vernon Wells would catch. "But he got enough of it," the pitcher said.
Latos (7-4) retired the first 11 Toronto batters before allowing four straight Blue Jays to reach base during a two-run rally in the fourth. Latos allowed two runs and four hits in 6 2/3 innings, struck out seven and walked one. He and three relievers combined on a five-hitter.
"I felt the ball kind of jumping out of my hand on every pitch," Latos said.
"He had great stuff tonight," manager Bud Black said. "That's the type of stuff we've seen the last six weeks. Maybe just a touch more velocity tonight early on."
Latos is 6-1 with a 2.05 ERA in his last eight starts.
Cecil (7-3) had his five-start winning streak snapped. He allowed five runs and seven hits in six innings. It was the second time in 11 starts he's allowed more than four runs.
Denorfia hit a sacrifice fly in the third and San Diego added three runs in the eighth, including two on David Eckstein's single.
Latos ran into trouble with two outs in the fourth inning. Adam Lind hit a slicing liner down the left-field line that dropped in for a double. Latos hit Wells with a pitch and Alex Gonzalez and Lyle Overbay followed with RBI singles that pulled the Blue Jays to 5-2. Latos then retired the next seven batters, starting by striking out John Buck to end the fourth.
Cunningham is the first player to get a grand slam for his first hit as a Padre, according to research by the Elias Sports Bureau. ... Blue Jays manager Cito Gaston said RHP Dustin McGowan, who has been sidelined since July 2008 because of shoulder surgery and a subsequent knee injury, will see a team doctor before being examined by noted orthopedic surgeon Dr. James Andrews. McGowan heard a pop in his shoulder while pitching at the team's minor league complex on Sunday and was shut down after eight pitches. He had an MRI exam on Monday.