SAN FRANCISCO -- Rockies right-hander Jason Marquis has struggled lately, giving up five or more runs in three of his last four outings.

The Rockies, of course, would rather have smoother work from Marquis. With Aaron Cook and Jose Contreras battling injuries, Marquis is the veteran leader of the staff. So how does Marquis become the pressure pitcher the Rockies need?

His answer is to concern himself with the pitching, not the pressure.

Marquis believes the problem is a flaw in the early part of his windup, not something related to the importance of games. As long as he can pinpoint the physical reason why his pitches are awry, and he believes he has done that, quality pitching will follow.

That's the hope for him and the Rockies going into Friday night's opener of a three-game set with the D-backs, as the Rockies attempt to protect their lead in the National League Wild Card standings. Wednesday night's thrilling 4-3 victory over the Giants gave the Rockies a 3 1/2-game lead over the Giants and a 4 1/2-game lead over the surging Marlins.

Marquis had slightly out-of-kilter mechanics and totally off-kilter pitch selection in his last start, when he gave up five runs in 5 2/3 innings of a 7-3 loss at San Diego. He can take care of pitch selection only in game action, but he concentrated on correcting the flaw -- not having his right foot in the proper position to generate power toward the plate.

"The day after my start this time just playing catch, I was able to feel something that I want to make a change on," Marquis said. "The first few throws of my bullpen, it felt right. Now it's just a matter of executing throws within that delivery."

At this time of year, the talk is usually of big games, not little delivery tweaks. But Marquis, a veteran of big games late in seasons, said the little fundamentals win big games.

He'll have to find those basics again. Since going 2-2 with a 1.93 ERA in July, Marquis is 3-4 with a 4.50 ERA.

"I try not to focus on results because you really don't control them," Marquis said. "What I control is the pitches, the execution of pitches and the pitch selection."

Pitching matchup
COL: RHP Jason Marquis (15-11, 3.78 ERA)
Marquis faltered against a team he had handled well this season when he allowed five runs to San Diego on Sunday as the Rockies fell, 6-3, in the series finale. In his previous two starts against the Padres, Marquis yielded just one run over 16 innings, but San Diego touched him for three runs in the decisive sixth after he walked Everth Cabrera with the bases loaded, one of three unintentional walks in the inning. After having his start bumped up one day but still pitching on normal rest, Marquis faces an Arizona team that scored six runs against him in a loss on April 20.

ARI: RHP Kevin Mulvey (0-1, 11.88 ERA)
Mulvey's first Major League start did not go as he'd hoped. The right-hander allowed six runs on 11 hits in just four innings against the Brewers at Chase Field. Mulvey is taking the place of Yusmeiro Petit in the rotation likely for the rest of the season. The club wants to get a look at the right-hander acquired in the deal that sent Jon Rauch to the Twins. Mulvey is no stranger to being traded. A second-round pick by the Mets in the 2006 First-Year Player Draft, he was dealt to the Twins as part of the Johan Santana deal. Mulvey was 5-8 with a 3.93 ERA in 24 starts for Triple-A Rochester this year and has appeared in two games in relief for the D-backs since joining the team on Sept. 1. He made his big league debut on July 20 with the Twins.

Tidbits
Rockies third baseman Ian Stewart, who knocked his 24th homer of the season in Wednesday's 4-3 victory over the Giants, has five home runs in his last 10 games. ... Troy Tulowitzki's 27 home runs represent the eighth-highest total by a shortstop in National League history. ... The Rockies are 2-4 at Chase Field this season. All of those games took place in April.

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Up next
• Saturday: Rockies (Jason Hammel, 8-8, 4.38) at Diamondbacks (Max Scherzer, 9-9, 4.05), 6:10 p.m. MT
• Sunday: Rockies (Ubaldo Jimenez, 13-11, 3.55) at Diamondbacks (Dan Haren, 14-8, 2.79), 2:10 p.m. MT
• Monday: Off-day