After a sluggish start for both teams, the U.S jumped out to a 1-0 lead with a man advantage as Marek Hovorka was off for hooking.
Chris Bourque fed Troy Terry who drew the Slovak defence and dumped it behind him to a trailing Donato.
Donato, whose father Ted Donato played on the Olympic U.S. team in 1992 in Albertville, France, snapped it past Slovak goaltender Jan Laco.
"It feels pretty good," said Donato, who is one of four college players on the U.S. team. "It's not always about the goals and who scores it, but obviously getting a couple goals it definitely felt good."
The Slovaks, who stunned tournament favourites Olympic Athletes from Russia in their opener, levelled 25 seconds later, when Tomas Surovy chipped a soft pass out of the corner to Andrej Kudrna, who tipped it between U.S. goalie Ryan Zapolski's pads.
But it was Donato on the powerplay again who put the U.S. back ahead for good in the third period.
Set up on the goalline next to the left post, he took a pass from Mark Arcobello, stepped forward, spun and pulled the puck to his forehand in front of Laco and jammed it in.
"I'm not too worried about who scores the goals as long as we get the win," Donato said.
After blowing a two-goal lead in the third period to lose to Slovenia in overtime on Wednesday, Friday's performance showed U.S. coach Tony Granato his team had learned from that letdown.
"When you go through experiences, if you learn from them and you apply them the next time that happens in life or in a game, then it was worth the experience," Granato said.
"The experience we gained from losing that lead in game one was we had to play differently tonight."
"It wasn't a perfect game, but I thought it was solid."
Both teams are 1-1 in the tournament. The U.S. next play the Russians and Slovakia meet Slovenia, both on Saturday.
The men's Olympic tournament is being played without NHL players for the first time since 1994 after the league and International Olympic Committee failed to agree on covering players' travel and insurance costs.
(Reporting by Dan Burns,; editing by Ed Osmond)
