Cosart pitched six effective innings, but the rookie yielded a two-run homer to Adrian Beltre and the Houston Astros lost 4-2 to the Texas Rangers on Tuesday night.
"I thought command-wise, it was my best game of the year," Cosart said. "I had command of two pitches, fastball and curve, and didn't have to use my changeup. They couldn't sit on one pitch."
As for the pitch Beltre hit for his 26th homer?
"That pitch was at his head," Cosart said. "It wasn't even a strike."
Beltre drove a high curveball to the seats in right field in the sixth, lifting Texas to a 3-2 lead. Beltre also doubled and scored in the second for the AL West-leading Rangers, who moved 20 games over .500 for the first time this season.
Cosart bit down on his glove as Beltre's line drive headed over the wall. It was the first homer he's allowed in his 45 big league innings.
"I was hoping it wouldn't go out," he said. "It was only 360 feet, but there's that jet stream to right field here. He put a good swing on it, and hit a home run. That's what good hitters do."
It was the 160th hit of the season for Beltre, one short of Miguel Cabrera for the major league lead.
Matt Dominguez homered for Houston, which has lost seven in row and 13 of 14 against the Rangers.
Neal Cotts (5-2) struck out the first three batters he faced over 1 1-3 innings and was credited with the win. The lefty was the second reliever after Travis Blackley pitched four innings against his former team only a week after being traded to Texas.
Joe Nathan struck out the side in the ninth for his 37th save in 39 chances.
Cosart allowed four hits and walked three while his ERA increased from 1.15 to 1.60. It was the first time he yielded more than two runs.
The 22-year-old Cosart made his major league debut on July 12 at Tampa Bay and pitched eight scoreless innings in a 2-1 victory over AL Cy Young Award winner David Price. That's his only victory on the year, but he tossed six scoreless innings at Oakland in his previous start.
"He pitched tremendous," Astros manager Bo Porter said. "He pitched six innings and gave up a two-run homer. Outside that one pitch, he did what you should do."
Houston has scored only 20 runs in Cosart's seven starts.
The only score for the Astros this time came on a two-run homer by Matt Dominguez in the second off former Houston left-hander Travis Blackley, who allowed three hits in four innings in his Rangers debut a week after being traded.
Catcher Max Stassi made his major league debut for the Astros. He was the designated hitter after being recalled from Double-A Corpus Christi. The Astros put catcher Carlos Corporan on the seven-day concussion disabled list after he got hit by a foul tip on the mask the previous night.
After striking out in his first at-bat, Stassi singled twice.
Stassi didn't have much time to celebrate his first major league hit in the fifth. As he ran to second base on Brandon Barnes' ground ball, Stassi saw reliever Jason Frasor throw toward shortstop Elvis Andrus. The high throw sailed past Andrus, but Stassi didn't notice and Ian Kinsler tagged him out after he left the base.
"That was a mental mistake," Stassi said. "That never happened in my career, and it never will again. I lost track of the ball."
In the first, L.J. Hoes had a hard shot that ricocheted off Blackley's foot toward the third base line. Jurickson Profar made a barehanded grab and threw in one motion to retire Hoes.
Porter quickly came out to unsuccessfully argue with umpire Lance Barksdale that Profar's throw pulled first baseman Mitch Moreland off the bag. Under the expansion of video review planned for next season, it was the kind of challenge Porter may have won.
NOTES: The 23-year-old Dominguez has 17 homers. Only two Astros have had more homers in a season by age 23, including Cesar Cedeno with at least 22 homers in three different seasons (1972-74) before he turned 24. Jimmy Wynn hit 22 homers at age 23 in 1965. ... Beltre is hitting .434 (33 of 76) over his last 21 games, raising his season average 19 points to .326, third in the American League.