Coming off his shortest outing since 2004, when he lasted just 3 1/3 innings against Oakland last week, Webb (11-4) gave up five runs -- four earned -- and eight hits in seven innings. The 2006 NL Cy Young winner started the season 9-0, but is 2-4 with a 4.64 ERA since.
"It seems like the big inning has been the problem," Webb said. "If its one or two, it's not as big of a deal. But four or five runs in one inning is a bad inning. I need to cut down and try to minimize the damage."
The Twins have leaned heavily on the big inning during their six-game winning streak. They scored all five of their runs in fifth on Sunday, the fifth straight game they have scored at least four runs in an inning.
"That's fine," Twins manager Ron Gardenhire said. "However you want to get them in, that's OK."
Manager Bob Melvin's decision to start Conor Jackson -- the normal first baseman -- in left field played a role in the latest tough frame for Webb.
Jackson went 3-for-4 and scored a run, but made a crucial mistake when he lost a pop fly from Delmon Young in the Metrodome's white roof that fell in for a double and ignited Minnesota's five-run fifth inning.
"I can't fault him. He played the position pretty well, he just lost one ball in the roof," said Melvin, who made the move looking to maximize his offense. "We just couldn't nail it down after that and it just got out of hand, just like the previous games."
Playing the outfield in the Metrodome is particularly challenging in day games, when the light sky combines with the baseball-colored roof to give players fits.
Jackson, who has played just six games in left all season, became the latest victim when Young's pop fly landed about five feet away from him to give the Twins runners on second and third with nobody out.
"I'm sure I'm not the first one to do it here and I'm sure I won't be the last," Jackson said.
Buscher followed with a two-run single and Alexi Casilla added another two-run single as the Twins took a 5-3 lead.
Though still a little shaky in the field, Buscher is hitting .353 with 12 RBIs and six runs scored in 10 starts since he was called up. The Twins are 7-3 in those games.
Livan Hernandez (8-4) gave up three runs, one earned, and nine hits with five strikeouts in seven innings for the Twins, who have their longest winning streak since July 2006.
Joe Nathan worked the ninth for his 19th save in 21 chances.
"We're on a little bit of roll here," Twins manager Ron Gardenhire said. "We've had some fun. A lot of clutch hits coming all at once and we got them."
With one of the best arms in baseball, Young charged hard in anticipation of making a play on Jackson at home -- except he forgot to catch it. The ball squirted under Young's glove and rolled to the wall. Jackson and Reynolds scored, and Snyder wound up at third before scoring on a wild pitch from Hernandez.
"This is the toughest left field in the league. ... That's just the way it is in this Dome," Gardenhire said.
Jackson would surely agree, and the Diamondbacks' struggling offense couldn't muster any more as they lost for the sixth time in eight games and 17th in their last 23 away from home.
"We're definitely in a bad streak right now," Webb said. "It's got to turn around sometime and I would think it's got to be soon because it's been a rough six weeks or so for us."
Reynolds was back in the lineup at 3B after leaving Saturday night's game with a sprained right ankle. ... Twins 1B Justin Morneau extended his hitting streak to 11 games with a single in the eighth. ... The Twins won their 115th game in interleague play, third most behind the Yankees and Oakland with 119. The Twins also announced that utility man Nick Punto will be called up from the DL in time for Minnesota's road trip to San Diego Tuesday.