"I don't remember," he said. "I swear to God. I wish I could. Playoffs maybe. But I don't remember where."
Jake Marisnick also homered on Thursday in a 2-1 win over the Los Angeles Angels.
Beltran's previous homer for Houston came on Oct. 17, 2004, in Game 4 of the NL Championship Series against St. Louis, capping a postseason in which he hit eight homers with 14 RBI in 12 games. He then left as a free agent to sign with the New York Mets.
Beltran's home run Thursday came with one out and the first inning off Matt Shoemaker (0-1), and Marisnick's second homer this season made it 2-0 in the fifth.
Beltran has 422 big league homers as his 40th birthday on Monday approaches.
"I don't get caught up in homers," he said. "For me it's about trying to put up quality at-bats. I think if I put quality at-bats, I know those are going to come."
Lance McCullers (2-0) scattered three hits and struck out eight over 6 2/3 scoreless innings as Houston won for the seventh time in eight games.
"We had a couple chances but not a lot," Angels manager Mike Scioscia said. "He's pitched us tough in this park and we just haven't figured him out yet."
Chris Devenski allowed home run to Mike Trout starting the ninth inning and back-to-back singles with one out before fanning Cameron Maybin and Danny Espinosa for his first save .
At 11-5 the Astros are off to their best start since 2006. They lead the AL-West a year after a 7-17 start put them in a hole too big to climb out of last season.
Shoemaker allowed three hits and two runs while striking out seven in a season-high seven innings.
Trout's homer was the only extra-base hit on Thursday for the Angels, who have lost eight of their last nine games.
Beltran put Houston ahead with his first-inning homer. Alex Bregman doubled with one out in the second before Evan Gattis drew a walk. But they were left stranded as Shoemaker struck out Marwin Gonzalez as the first of 10 straight Astros he retired.
Houston didn't have another baserunner until Marisnick's home run made it 2-0 with two outs in the fifth inning.
McCullers plunked Kole Calhoun with one out in the first inning and walked Maybin with two outs in the second inning. The Angels didn't get a hit until Andrelton Simmons singled to start the fifth. But he was picked off trying to steal second base and McCullers retired the next two batters to end the inning.
McCullers was lifted after walking consecutive batters with two outs in the seventh inning.
Houston's Carlos Correa was 0 for 2 with a walk in his return to the lineup after sitting out three games with a sore right hand after being plunked on Saturday in Oakland.
Astros: Houston placed right-handed reliever Jandel Gustave on the 10-day DL with tightness in his right forearm and called up right-hander James Hoyt to take his spot on the roster.
Devenski, who pitched 2 1/3 innings on Thursday, has struck out 25 in 13 1/3 innings this season. The performance leaves him with a 1.35 ERA and a 16.88 strikeouts per nine innings ratio. It was his second career save, and he believes working through the jam in the ninth inning on Thursday will help him in the future.
"Big time going forward," he said. "Definitely something that I know what's that like now. Especially in a tight situation like that, so it was good."
THEY SAID IT
Trout on coming up just short on Thursday: "We had an opportunity. We just couldn't come up with the big hit. You've got to look at the positives. We've got a seven-game homestand (up next)."
Angels: Alex Meyer will be recalled from Triple-A Salt Lake on Friday to make his first start of the season when the Angels open a four-game series against Toronto. Meyer is 0-0 with a 4.80 ERA in three minor league starts this season.
Astros: Mike Fiers looks for his first win this season when he starts on Friday in the opener of a three-game series at Tampa. Fiers is 0-1 with a 5.40 ERA in two starts this season and allowed six hits and five runs in four innings in his last start.