Brandon Backe was at his best with runners on base. Good thing, too, because he put them there.

Backe worked around a career-high six walks and pinch-hitter Orlando Palmeiro homered to lead the Houston Astros past the Mets 4-1 last night.

“The amount of changeups that worked for me tonight really helped me out,” Backe said. “I just stayed away from the big inning. If I did walk a guy, I somehow got a strikeout or a groundball. I refocused and went after the next hitter.”

Craig Biggio and Jason Lane each had an RBI double for the Astros, who improved to 6-23 on the road and handed the Mets only their fourth defeat in 12 games.

New York lost star catcher Mike Piazza to a bruised left wrist in the first inning after he was hit by a foul ball. X-rays were negative and he was day-to-day.

“It’s swollen, but we’ll just go and see how it is tomorrow,” Piazza said. “On the base of the wrist, the left wrist, pretty flush, pretty square. I’ve had it on ice two or three times. Right away, it was bugging me and I just tried to get through the inning.”

Piazza’s replacement, Ramon Castro, came through with an RBI double in his first at-bat, but Backe (6-3) limited the damage.

Starting on three days’ rest after making his first relief appearance of the season Saturday against St. Louis, the right-hander gave up four hits in six innings. He struck out seven, helping him overcome a wild outing.

Chad Qualls and Dan Wheeler each threw a scoreless inning before Brad Lidge got three outs for his 14th save in 16 chances.

One night after Pedro Martinez pitched a gem against one of baseball’s worst offenses, Mets starter Victor Zambrano (3-6) allowed three runs and six hits in six innings.

The Mets took the lead in the first when Mike Cameron walked and scored on pinch-hitter Castro’s two out double. Marlon Anderson followed with a looper to center, but Lane made a diving catch to save two runs.

“When it came off the bat, I thought it was going to drop in there. It hung up there a little bit longer than I thought, and he made a great play. What can you do?” Anderson said.

Anderson started at first base for Doug Mientkiewicz (strained chest muscle, bruised ribs) for the second consecutive night.

The Mets stranded 11. They loaded the bases in the second, but Carlos Beltran grounded out.

“We had a couple of chances in the early innings but couldn’t get the big hit,” Anderson said.

Todd Self singled in the fourth and scored on Biggio’s double to left, tying it at 1.

Zambrano walked Self leading off the sixth, and Biggio followed with a single. After a double play, Zambrano had a chance to escape unscathed, but Morgan Ensberg drove in the go-ahead run with an infield single down the third-base line.

“We got a lot of contributions from a lot of people,” Biggio said. “We didn’t get a ton of hits, but we got big hits.”

Lane added an RBI double to make it 3-1, and Palmeiro connected in the seventh off Heath Bell for his third career pinch-hit homer.