Ahmed came in with his arms raised up, and was hit by Nix's throw. The ball rolled away, allowing Tuffy Gosewisch to score the winning run.
"That's the way we're taught to slide and play the game. Go in hard and late and it wasn't a dirty play in my mind at all," Ahmed said.
Manager Clint Hurdle and the Pirates lingered on the field to argue with the umpires, to no avail. There was no video review of the final play, and crew chief Ron Kulpa said the call couldn't be challenged.
After the game, the umpires looked at a replay for their own sake. Second base umpire Lance Barrett stood by his no-call on interference and Kulpa backed him.
"The guy has to do something obviously, willfully, intentionally to break up that double play. Guys slide into second base all the time with their hands up," Kulpa said.
"When Lance told him what he had, we talked about it, but Clint wasn't very irate. It's a big play. We looked at the tape, and Lance got it right," he said.
Hurdle felt otherwise.
"I felt there was an extra effort in getting his hands up, in the way," he said.
Ahmed had a bandage over his arm after the game.
"I was anticipating if the ball was on the ground trying to go in hard and breaking up two," Ahmed said. "I went in hard and slid late, and it looked like Nix kind of dropped down to try to make the throw and it just hit me in the arm."
Gosewisch doubled with one out in the 10th and Ahmed walked. A wild pitch by Mark Melancon (1-3) moved Gosewisch to third.
McCutchen left the game moments later with left side discomfort.
The Pirates signed Nix before Sunday's game. He was released by Tampa Bay on Friday and also played for Philadelphia earlier this season. Nix entered the game in the eighth and soon was involved in the key play.
The Pirates optioned infielder Brent Morel, who went 2 for 2 with three RBIs in Saturday night's 8-3 win over Arizona, to Triple-A Indianapolis. He was 3 for 16 in nine games with the Pirates.
Pirates: Second baseman Neil Walker missed a second straight game with lower back tightness. He'll get one more day of rest with the Pirates getting Monday off and is expected to be ready to play Tuesday against Miami. ... Outfielder Starling Marte went 1 for 4 in a rehab game with Triple-A Indianapolis on Sunday. He's coming back from a concussion.
Diamondbacks: Outfielder Cody Ross went swimming in a pool on Saturday, but is still a ways off, manager Kirk Gibson said. Ross has been on the disabled list since July 22 with a left calf injury. ... Outfielder A.J. Pollock (hand) doubled in two at-bats in a rookie league game Saturday and could soon be sent to Triple-A Reno to continue his rehab.
Pirates: After an off-day Monday, right-hander Charlie Morton gets the call against the Marlins in Pittsburgh on Tuesday. Morton has worked at least seven innings in eight starts this season. He's 5-3 all-time against the Marlins.
Diamondbacks: Left-hander Wade Miley (7-7) starts the opener of a three-game home series against the Kansas City Royals on Tuesday. He's 4-1 in his last six starts and the teams is 4-0 in his last four home starts.
Copyright by STATS LLC and The Associated Press
PHOENIX, AZ - AUGUST 03: Josh Harrison #5 of the Pittsburgh Pirates warms up on deck during the MLB game against...