"[The doctors] are pretty confident that they got her to the hospital in a shape where they could treat her and get her well again," said Russ Amaral, a D-backs vice president in charge of facilities and event services.
Joyce, who was scheduled to work the game behind the plate, arrived at the ballpark around 5:15 p.m. MST. He was walking down a ramp that leads to the umpire's dressing room.
Nearby, a briefing to the Levy food service workers had just broken up, and Powers, who has worked for the D-backs since their inaugural season in 1998, was speaking with a co-worker. She suddenly grabbed her co-worker's arm, began to shake and then fell to the ground.
"I knew something was wrong," Joyce said. "And I knew if something wasn't done, this lady could actually die in front of me. It was more instinct than anything else."
Joyce began to perform CPR, something he learned in high school.
"I've always stayed up with it," Joyce said. "Everybody should know it. I truly mean that. Everybody should know it. Because if you only have to use it one time, it can, well ... you can see what happened."
Not long after, Marlins bullpen coordinator Jeffrey Urgelles arrived on the scene. Urgelles was a firefighter/paramedic in the Miami-Dade County area. He assisted Joyce and later also helped out the paramedics.
"Somebody called for a trainer," Urgelles said. "I saw one of the security guys sprinting up the stairs. I knew then something was up, and I started walking out of the cage to see what was happening. Ricky Nolasco screamed for me. He was saying, 'Urgy, Urgy, they need someone who knows CPR.'
"I ran down the hallway and the lady was down on the ground. When I got there, there was a lady down and two people there. One of the guys was doing compression. That man ended up being Jim Joyce, the umpire. Until then, I didn't know who he was until late last night."
A call had already been made to the D-backs' security control room to send help, and a first responder arrived on the scene within minutes with an automatic external defibrillator (AED). Joyce continued with the CPR while the first responder worked with the AED.
Some 20 minutes later, Powers was transferred to an ambulance, which took her to Good Samaritan Hospital, where she finally regained consciousness.
Joyce, meanwhile, went to the umpire's room to get ready for the game. His fellow umpires offered to let him work third base, a less strenuous assignment rather than working the plate.
Joyce turned them down flat.
"I couldn't stand on third base and think about it all night," Joyce said. "And my job is to do my rotation in the crew, and nothing would have kept me from working the plate last night. Not only that I could get my mind off it because there's action on every pitch."
D-backs executive Roland Hemond called Joyce over to the screen behind home plate during the game to let him know that Powers had regained consciousness and looked like she was going to be OK.
"Obviously I wanted to know, unless it had been bad news," Joyce said. "My wife actually told everyone if it's bad news, you don't tell him. Because I wouldn't have been able to continue."
By Tuesday morning, Powers was doing better and doctors told D-backs officials that she might be able to go home later this week.
"The doctors have said, 'I'll tell you what -- if it wasn't for the first person who was on scene and the fact that you had those AED's, there's a very fairly decent chance this would not have turned out well, and she might not have made it to the hospital at all,'" Amaral said.
The D-backs have AED's at different locations throughout the ballpark and have trained various front-office and event-staff members on how to operate them.
Until Monday, though, they had never been used.
"You never know how people are going to respond until they have to use it," Amaral said. "Thank God we purchased these things."
Joyce and his wife, Kay, visited Powers on Tuesday, and when the umpire walked into the room, he was so overcome with emotion, he was unable to speak.
"Thank God my wife Kay was with me, because she interpreted," Joyce said.
While he was performing CPR, Joyce was singing the song "Staying Alive" as a way of keeping the compressions going at the right time.
Joyce asked Powers if she remembered him singing to her.
"She didn't remember that," Joyce said. "But she told my wife she remembered my voice. I was yelling for her to come back and everything. She said she recognized my voice, so that's really kind of cool."
A big league umpire for 24 seasons, Joyce gained notoriety in 2010 when his missed call at first base cost Detroit's Armando Galarraga a perfect game.
Certainly Powers and the entire D-backs' organization will now remember him for an entirely different reason. As he prepared to work Tuesday's game, Joyce was stopped by D-backs day of game employees and front-office personnel. Everyone, it seemed, wanted to thank him for what he had done.
"I'll be very honest with you," said Joyce, who teared up at times while being thanked. "The way I look at it is, somebody needed help and I was fortunate enough to know what to do. I just looked at helping someone who really needed it. She was in bad shape and needed help."