Robert Galbraith / Reuters

Barry Bonds smashes a home run off Mets pitcher Tom Glavine on Tuesday. The Giants, however, lost 4-1.

Beltran cut his teammates’ hair in the clubhouse bathroom before batting practice, and almost everyone took part. Manager Willie Randolph closely monitored the entire operation, his hair already trimmed close to the head.

Glavine got a special reprieve simply because he was pitching, though the left-hander said he was in no way against doing something so silly in order to bring players closer.

“It’s not part of my pregame ritual,” he said.

And that ritual has worked well for years now.

“It’s unbelievable,” Randolph said of Glavine. “He’s amazing. He goes out there and keeps you in a game, makes adjustments and continues to show why he’s one of the best in the game.”

Cain lost his second straight start, allowing four runs and a season-high 10 hits in seven innings. He struck out four and walked one. The 22-year-old right-hander has surrendered 18 total hits in his first two May starts after giving up only 12 hits over five April outings.

He ended April with a 1.54 ERA — third-lowest in the National League — but it has since risen to 3.40.

Notes: Glavine won his 20th game against the Giants. ...Cain was 2 years, 320 days old when Glavine made his debut in 1987. ... Giants CF Dave Roberts missed his third straight game with an inflamed left elbow — and the club was discussing placing him on the DL as soon as Wednesday. The injury is on his throwing arm, making it painful not only to throw but also to hit. ... Mets RHP John Maine celebrated his 26th birthday.