Coming into the contest, Leake held the seventh-longest active streak in the Majors by not having surrendered a home run in 45 2/3 innings dating back to April 26. That all changed when Michael Morse connected for his second homer in as many games, a 428-foot smash into the second deck in left field to give the Giants a 2-1 lead in the second.
Following singles by Pablo Sandoval and Tyler Colvin in the fourth, Leake gave up another home run, this time a 387-foot shot to right-center by Brandon Crawford, which made it 5-1.
"Truth be told, ever since the Cardinals start he's been battling with some stiffness in his neck," Reds manager Bryan Price said. "So he hasn't been able to get that head turned all the way to the catcher's glove. ... He just wasn't executing to the same degree today. ... I got him out of there because it didn't seem like things were going to get any better."
Leake had been 4-0 with a 0.92 ERA in his prior four starts against San Francisco before getting roughed up in his shortest outing of the season. He said that the stiff neck wasn't the cause of his problems, just poor pitch location.
"I'd just say that last little extension is tough to get [because of the neck stiffness]," Leake said. "But I'm still able to throw balls where I want to for the most part, and today it was just the first game I think I haven't been able to. The neck was fine today; there weren't any issues."
Price knew Leake might downplay the neck issue, but said he had to take the right-hander out of his previous two starts because of it.
"We've needed him to pitch and he's comfortable to pitch, but he's not 100 percent, by any means," Price said. "He may make nothing of it and that's the type of kid he is, but we've taken him out, I think, the two previous starts because of it, just because it got to the point where it really stiffened up."
The Giants added a run in the seventh, when Buster Posey grounded an RBI single into left against Reds reliever Sean Marshall to extend San Francisco's lead to 6-1.
The Reds scored their only run of the contest on a homer by Todd Frazier in the first inning off Bumgarner. It was Frazier's team-leading 12th home run of the season and his third in the past four games.
After Frazier hit a two-out single in the fourth, the Reds did not manage a hit the rest of the way, as Bumgarner retired 16 straight before giving way to George Kontos in the ninth.
"We seemed to have a really nice approach in that first inning, and we just weren't able to maintain it," Price said of Cincinnati's offense. "I don't know if [Bumgarner] got better or if we lost the approach. I'm not sure, but we just weren't able to string anything together against him."
Bumgarner agreed, crediting early recognition of the Reds' aggressiveness at the plate and making adjustments accordingly.
"They've got good hitters, they've got an offensive ballpark, and they came out aggressive," Bumgarner said. "It was obvious they were coming up there to swing. We made some adjustments and our defense made some really great plays."
After scoring 23 runs in four games, including the series opener with San Francisco on Tuesday, the Reds have managed only three over their last two contests.
"I'm not disappointed or starting to think we saw the best of our club and now we're back into the doldrums," Price said. "But certainly I thought with the approach we had today that we were going to do more damage than we did. We came out smoking in that first inning, and then that was it other than Frazier getting a hit his second time up."
There were a few balls stroked by the Reds that may very well have been hits, but the Giants made some excellent defensive plays, including a diving catch by right fielder Hunter Pence to rob Billy Hamilton of extra bases in the first inning.
"I felt like we did not do a real good job of hitting, but we did some things and they made some real good plays," Hamilton said. "Crawford made a couple plays, Sandoval made a few good plays. They made some great plays in the field."
Hamilton, like Price, doesn't believe Cincinnati's struggles over the past two games are any reason to lose confidence that the recent success that the Reds experienced in the four games prior remains a sign of things to come.
"I still feel like we have confidence even after losing these two games," Hamilton said. "We won some on the road before this happened, but I feel like the guys are still up, and we still have that confidence that we can start winning some more games."
The Reds will get a chance to do that when they welcome the Phillies to town for a three-game set beginning Friday, trying to snap a streak of three consecutive home series losses and rebuild momentum after San Francisco put up a roadblock.