Evan Longoria, Thairo Estrada, Joc Pederson and Wilmer Flores homered for the Giants, who snapped a three-game skid. They had lost five of six after winning seven of their previous eight.
Brandon Drury homered for the Reds, who have lost eight of their last nine games.
''That's the team that we expect ourselves to show up every single night,'' Webb said. ''Sometimes you go through a rough patch, and unfortunately, it's just lasted a longer than we hoped.''
Cincinnati took advantage of Giants third baseman Longoria's two-out fielding error in the top of the second to take an early lead on Nick Senzel's run-scoring single.
But Longoria homered leading off the bottom of the inning and Estrada went deep two batters later to give San Francisco a 2-1 lead.
Longoria turned on a 2-2 inside fastball off Reds starter Mike Minor for his seventh home run, a 411-foot shot to left.
Darin Ruf's run-scoring single highlighted a two-run third that gave San Francisco a 4-1 lead.
Pederson hit his 17th homer off Minor - his second off a lefty this season - leading off the fifth.
Flores' two run homer - his ninth - highlighted a three-run sixth in which the Giants broke open a 6-1 game.
''I thought the Flores homer was the one we've been waiting for,'' Giants manager Gabe Kapler said.
''We've talked about one more really good at-bat in the game to make the difference, we've also talked about how big innings win baseball games for us . that's been one of the keys to our success.''
Webb (7-2) struck out six and walked two. He's given up just two earned runs over 18 innings over his last three starts.
''(Webb's) sinker moves a lot, it's very heavy, it didn't like the 92-93 (mph) that the radar was saying,'' Drury said.
''It felt harder, and he was throwing a lot of changeups and sliders, so it was just hard to be on time for the sinker when he wasn't throwing a lot of sinkers and when you start thinking soft, he puts the sinker on your hands. It was just tough. He was really good today.''
The Giants have won 22 of Webb's 28 career home starts.
Minor (1-4) gave up six runs on eight hits including three home runs in his fifth start after missing the first two months with a shoulder injury.
''I know he's doing everything he can . just wasn't able to execute the pitches the way he knows he needs to,'' Reds manager David Bell said of Minor.
''All you can do is continue to search, continue to work, and I know he's doing that, but I know it's frustrating for him also.''
The Giants ended a streak of 10 straight games decided by two runs or less, the longest such streak in the team's San Francisco-era history.
The Reds claimed C Michael Papierski off waivers from the Giants. The Giants had just acquired the 26-year-old from the Houston Astros in exchange for infielder Mauricio Dubon. The Reds optioned Papierski to Triple-A Louisville.
Reds: C Tyler Stephenson is progressing faster than expected from a right thumb fracture he sustained June 9 and could start a rehab assignment in the next seven to 10 days, manager David Bell said Saturday. . RHP Vladimir Gutierrez (right forearm) threw a bullpen Friday and could be ready to be activated soon, Bell said. OF Aristides Aquino (left high ankle sprain) is expected to resume baseball activities Monday, Bell said. 2B Jonathan India appeared to be hurt after being struck by a pitch leading off the fifth off Webb, but he stayed in the game until the eighth, when he was lifted for a pinch hitter. . The Reds have 15 players on the injured list.
Giants: SS Brandon Crawford (bruised left knee) was out of the lineup Saturday for the third time in four games. He played Friday for the first since suffering the injury Tuesday in Atlanta during a collision at home plate. ''I don't think he felt great yesterday, but this is not anything but trying to get him healthy and just confident. Health first. We're trying to get him over the hump with the health stuff.''
Reds RHP Tyler Mahle (2-6, 4.57 ERA) has thrown six straight quality starts but is winless since May 13. Giants RHP Anthony DeSclafani (0-1, 7.71) gave up six earned runs in three innings Tuesday against Atlanta in his first appearance since coming of the injured list with right Achilles inflammation.
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