Plate umpire Chad Fairchild called Donaldson out, and Melvin instantly ran out to challenge. Not only was it tough to tell whether Donaldson beat the tag, but it was also unclear whether Iannetta might have illegally blocked the plate with his left foot.
"We thought he got his hand in there," Melvin said after the game. "I still haven't seen the replay. I saw the one on the scoreboard, and it looked like he was safe."
The A's did not score in the inning, and the Angels tied the score in the seventh, but Oakland pulled ahead in the eighth to win, 2-1.
In the third inning, Angels manager Mike Scioscia was successful with his challenge on an out call at first base, rewarding Albert Pujols with an infield single.
Pujols was out in front on a Jon Lester breaking ball, hitting a blooper in front of second base with some backspin. Second baseman Alberto Callaspo, shifting to the left side against Pujols, ranged to his left, fielded the ball cleanly and fired to first, but Pujols hustled down the line and made it just ahead of the throw.
First-base umpire Mike Everitt called him out, but Pujols urged Scioscia to challenge the play, and umpires ultimately reversed their decision. The Angels are now 15-for-26 in challenges this season.
Pujols was stranded on first after Josh Hamilton struck out to end the inning.
Aaron Leibowitz is an associate reporter for MLB.com. Alden Gonzalez is a reporter for MLB.com. Read his blog, Gonzo and "The Show", and follow him on Twitter @Alden_Gonzalez. This story was not subject to the approval of Major League Baseball or its clubs.