This is the 28-year-old's first career Pitcher of the Month Award.
The Majors' home run champ from a season ago (54), Bautista led the AL in April with a .366 average and nine homers. He also led the Majors with a .532 on-base percentage, a .780 slugging percentage, 28 walks and 25 runs scored.
The 30-year-old carried two six-game hit streaks, and was hot from the first day of the season, when he went 3-for-4 with a homer and three runs scored against the Twins in a 13-3 victory.
A Silver Slugger and Hank Aaron Award winner last season, Bautista finished the month strong, hitting six homers in his last 11 games. Bautista was named Player of the Month three times in 2010 in May, July and August.
Bautista finished fourth in the AL MVP balloting last season.
As good as Weaver's been to start the season, his manager thinks he was just as good last season, when he went 13-12 with a 3.01 ERA and a Major League-best 233 strikeouts.
"There's not much different that he's doing now that he didn't do last year," Angels manager Mike Scioscia said. "Outside the wins and losses, his internal numbers matched up with any Cy Young candidate. He's very pitch-efficient, plus he's been able to carry some deep pitch counts and maintain his stuff, so he can pitch deeper in games."
Weaver went 6 1/3 innings in a 4-2 win over the Royals on Opening Day, but that was just the tip of the iceberg. In his first home start of the season, he fanned a career-high 15 batters in 7 2/3 innings to lead the Angels over Bautista's Blue Jays, 3-1. It was just the 14th time in Major League history that a pitcher recorded 15 or more strikeouts in fewer than eight innings pitched.
No Angels pitcher had reached the 15-strikeout plateau since Mike Witt recorded 16 strikeouts on July 23, 1984.
Both players receive trophies commemorating the award. The Yankees' Robinson Cano and the Royals' Alex Gordon were also top vote-getters in the Player of the Month selection, as voted on by writers around the league. Weaver's teammate Dan Haren and Oakland's Trevor Cahill also received votes in the pitcher's award voting.