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PHOENIX -- With his team on a six-game losing streak, Arizona ace Brandon Webb felt a sense of urgency as he took the mound.

"Every win right now is a must-win for the whole team," Webb said.

Webb tossed eight shutout innings to become the National League's first 20-game winner and the Diamondbacks beat the Cincinnati Reds 3-2 on Friday night.

Webb (20-7) outpitched Aaron Harang to earn his first victory since Aug. 21. Arizona remained 3 1/2 games behind the NL West-leading Los Angeles Dodgers, who won 7-2 at Colorado.

Arizona's shaky bullpen nearly blew Webb's victory in the ninth. Closer Brandon Lyon gave up four base hits, including a two-run single by pinch-hitter Jeff Keppinger, before manager Bob Melvin summoned Chad Qualls.

"At that point, I had given [Lyon] enough rope, and I needed to go get him," Melvin said.

Qualls entered with runners on first and third, and struck out pinch-hitter Jerry Hairston Jr. for his third save in 11 chances.

Lyon also blew a save in a wrenching loss at San Francisco on Wednesday, and Melvin hinted he may make a switch at closer.

"Tomorrow, we'll deal with some of the issues that we need to take care of," Melvin said.

The Diamondbacks seemed more relieved than excited as they exchanged high-fives after the final out.

"Hey, a win's a win," Melvin said. "That's what we talked about earlier today. That's what we were looking to do was win a game, and we did."

Webb, who won his first nine starts, had pitched poorly in his first three attempts at his 20th victory, allowing 19 earned runs in 13 2-3 innings.

Asked if his quest for 20 victories had been weighing on him, Webb said: "It was starting to a little bit, I think. I've gone through slumps and stretches, not really as bad as what I've had in the last few outings."

Webb pitched efficiently, throwing 58 of his 96 pitches for strikes. He had much sharper command than he had in recent starts.

"It feels good to finally get there," said Webb, the 2006 NL Cy Young Award winner. "The team needed a win, and I needed to get off my slump and get back to where I usually am."

Webb became Arizona's first 20-game winner since 2002, when Randy Johnson won 24 games and Curt Schilling won 23.

The Diamondbacks broke up a scoreless tie in the sixth, and Harang (4-16) had only himself to blame.

With one out, David Eckstein hit a high chopper that Harang fielded behind the mound. Though he appeared to have little chance to get the speedy Eckstein, Harang whirled and threw down the right-field line, allowing Eckstein to race to third.

Eckstein, acquired from Toronto on Aug. 31, snapped an 0-for-19 slump with the infield single.

On the next pitch, Chris Young singled through the left side of the drawn-in infield to give Arizona a 1-0 lead.

The Diamondbacks added two runs in the eighth when Bill Bray walked former Reds slugger Adam Dunn with the bases loaded and Eckstein scored on a wild pitch by Mike Lincoln.

"We made some mistakes tonight that cost us," Cincinnati manager Dusty Baker said. "We gave them every run. We beat ourselves tonight."

Webb allowed five hits, struck out two and walked two.

Harang gave up an unearned run and four hits in seven innings. He retired the first nine Diamondbacks before Stephen Drew led off the fourth with a single.

"Just how I felt overall, that was one of my better outings probably this year," said Harang, who has one victory since June 13. "I was executing my pitches and getting ahead early. That's the key to trying to beat a good team."

Game notes

Arizona LF Conor Jackson had an MRI on a sore right shoulder. Melvin said the tests showed no structural problems and Jackson could return to the lineup in a few days. The Diamondbacks started Dunn in left. ... Arizona LHP Randy Johnson, who missed a turn with a sore shoulder, will start on Saturday night. He's six wins away from 300 and is scheduled to make four more regular-season starts.