(Sports Network) - Streaking Colorado right-hander Aaron Cook makes his 20th career appearance against the Arizona Diamondbacks tonight, when the Rockies host their National League West Division foes at Coors Field for the middle test of a three-game series.

The Rockies won the opener, 5-0, on Friday with a combined four-hit shutout from starter Jorge De La Rosa and relievers Joel Peralta and Huston Street.

Colorado enters the game third in the West, trailing first-place Los Angeles by 8 1/2 games, but entering just a game back of NL wild card-leading San Francisco.

The Diamondbacks, meanwhile, are 20 games out of first place and have the second-worst record in the league.

Cook, a native of Fort Campbell, Kentucky., was just 3-3 after consecutive losses to the Dodgers and Houston Astros on May 26 and June 1. He was unbeaten in his subsequent June starts, winning five straight while allowing just seven runs in 36 innings.

Most recently, in an interleague game at Oakland on June 28, he surrendered just nine hits and a run in eight innings of a 3-1 triumph.

He's 5-4 lifetime against the Diamondbacks in 19 appearances - 17 starts - with a 5.53 earned run average in 107 1/3 innings.

Included is his 2009 season debut in Phoenix, in which he got a no-decision after being ripped for seven hits and six runs in just 2 1/3 innings.

For Arizona, right-hander Yusmeiro Petit returns to the mound for the first time in nearly two months.

The 24-year-old Mexican export was shelved following a 5-4 loss to Washington on May 8, sustaining a strained right shoulder.

In five rehabilitation starts for Triple-A Reno, Petit was 0-1 with a 6.89 ERA.

He faced the Rockies on April 21 in his third outing of the season, getting a no-decision in a 9-6 loss.

The Diamondbacks are winless in six games he's pitched.

On Friday, De La Rosa (5-7) won his third straight start by allowing four walks while striking out six. Peralta and Street combined to hurl a perfect ninth for the Rockies, who were coming off a 5-4 road swing.

Chris Iannetta and Troy Tulowitzki each had two hits and an RBI, and Ian Stewart added a solo homer for the winners.

Max Scherzer (5-6) suffered the loss, allowing five runs -- three earned -- on six hits and a walk, adding five strikeouts in his six-inning start for Arizona, which had almost as many errors (three) as hits (four).

The D-Backs went 15-3 against the Rockies last season, including a 7-2 mark in Denver.