DENVER -- Padres manager Buddy Black, who started 296 games in the Majors, sees the benefits of the Rockies curious four-man starting rotation.

"[The other team] has to be prepared for the reliever," Black said. "If you have a heavy right-handed lineup against a left-handed pitcher, then before you know it you've got a right-handed pitcher in behind him. Those matchups might not come in play as much if they're using four to five guys a night."

The exact situation was a possibility on Friday for the Rockies, who started lefty Jeff Francis. After Francis' 75 pitches are thrown -- each of Colorado's four starters are on a 75-pitch count -- then right-handed Tyler Chatwood is expected to come in.

Since going to the four-man rotation on June 19, the Rockies were 4-6 entering Friday's game, with an ERA of 5.99 -- a shade better than the full-season 6.53 mark for all Colorado starters.

"The Rockies know their personnel better than anybody," Black said. "I'm sure they thought this out and thought it was the best thing to do for their club."

Cashner's start made deep impression

DENVER -- In his second start of the season on Friday night, San Diego's Andrew Cashner held the Astros hitless through 6 1/3 innings, striking out nine batters.

"I felt like I had better stuff when I was in the Minors and tonight I felt like I still had my fastball there in the seventh," said Cashner, who has come on in relief in 27 of his 29 appearances. "I feel like my legs are really strong right now and I can hold my velocity."

The right-hander had his no-hit bid broken up in the seventh on a single by Carlos Lee and later allowed a homer by Brian Bogusevic that chased him from the game.

The 6 1/3-inning outing was the longest of Cashner's career and four innings more than his season high. Cashner threw 101 pitches, more than double his previous season-high (47).

"He came out good," Black said on Friday, before the Padres began a three-game series at the Rockies. "But I wouldn't pitch him today."

Cashner even eagerly suggested he'd be able to run the bases Friday, if needed.

"That was our conversation about how he felt, went right into pinch-running," Black said with a laugh.

Worth noting

• John Baker started Friday at catcher in place of Nick Hundley. Black listed Hundley's trouble against lefties (.108 season average) and fatigue as reasons.

"Nick caught three of the four games [in Houston] and I want to give him a day away from starting," Black said. "And Baker's had some good at-bats lately. You gotta use your whole roster."

Baker is hitting .321 (9-for-28) in his past 10 games prior to Friday.

• With his go-ahead grand slam on Thursday against Houston, Alexi Amarista became the fifth Padre in team history to hit a grand slam for his first Major League homer and the first since 2002 (Ramon Vazquez).

• Third baseman Chase Headley entered Friday's game with a .329 batting average (25-for-76) in his last 20 games. Headley leads the Padres in hits and RBIs.

• The Padres were 3-3 against the Rockies this season entering Friday, with a 1-2 record at Coors Field. Sixteen games back in the National League West, the Padres trail Colorado by just two games.