McDonald redeemed himself after hitting the crossbar early in the game.
"I didn't really get a good shot off," he said of his miss. "Sometimes you don't get those scoring chances [again], and I was fortunate to get more good scoring chances in the second."
His back-to-back goals in the period brought the Ducks back from a 1-0 deficit, then he assisted on Dustin Penner's game-winner in the third.
The only team to overcome a 3-1 deficit in the Finals was the 1942 Toronto Maple Leafs against the Detroit Red Wings.
"If we play like we did for two periods tonight, [our chances] are not very good," Ottawa coach Bryan Murray said. ". . . Walking around goals and two-on-one goals, those are bad goals to give up during playoff time."
Four minutes into the final period, the Ducks mounted an odd-man rush and Teemu Selanne made a slick pass to Penner, who scored the game-winner easily.
McDonald, one of the heroes of Game 1, pushed the puck up the ice under pressure from Wade Redden to set up the goal.
"It was a line change and the puck was inside our own blue line," Penner said. "Mac made a strong play at the blue line to get it out to Teemu."
The Ducks also received sensational play from goalie Jean-Sebastien Giguere, who made 21 saves, including 12 in the first period when he was under siege. Anaheim played without defenseman Chris Pronger, who was suspended for a vicious elbow to the head of Dean McAmmond in Game 3.
McAmmond was sidelined with concussion symptoms. Mike Eaves took his spot and assisted on Ottawa's second goal. Ex-Flyer Joe DiPenta replaced Pronger in the Ducks' lineup, although he didn't play much. Pronger's playing time was gobbled up by Scott Niedermayer (29 minutes, 33 seconds) and Francois Beauchemin (31:40).
"We don't want to get used to playing without Chris," Scott Niedermayer said. "He's a great player and helps our team a lot. When he is not there, we realize we have to do our best."
The Senators swarmed the Ducks in the first period, outshooting them by 13-2. During two power plays, Giguere made some incredible chest and pad stops on Andrej Meszaros, Dany Heatley, Antoine Vermette and Redden.
"We did the same things as Game 3 - taking penalties and not making good decisions with the puck breaking out of our end," Scott Niedermayer said. "Being down by one goal after that, we were lucky."
With three-tenths of a second left in the first period, Daniel Alfredsson scored a power-play goal for Ottawa on a measured shot off a pass from behind the net by Peter Schaefer.
Murray was asked how his team could be so dominant early and then collapse. "I don't know exactly," he said. "We played well and didn't get rewarded until the last second in the first."
The Ducks dominated the second period although their power-play ineptness continued, too, as they failed on two chances. Anaheim is 1 for 14 with the man advantage in the series.
McDonald missed tying the game three minutes into the second stanza when his chip shot in the crease kissed the crossbar.
Then came his first goal on a shot under the bar at 10:06. A minute later, McDonald scored his ninth goal of the postseason.
Taking a Rob Niedermayer pass into the zone and up the middle, the fluid winger cut left to right around Ottawa's intimidating defenseman, Anton Volchenkov, then backhanded the puck from the right crease to the opposite post on Ray Emery for a 2-1 Ducks lead.
Emery prevented it from becoming 3-1 with a nifty glove save on Beauchemin. That allowed Heatley to tie the game in the final two minutes of the period with his first goal of the series.
Online extra: The NHL takes aim at blows to the head.
Contact staff writer Tim Panaccio at 215-854-2847 or email@example.com.