The Memorial is one of the most prestigious events on the PGA Tour and Hovland received a prize cheque of SEK 39 million.
"It feels unreal, to play on Jack's court and win his tournament," Hovland said on Discovery's broadcast.
"The fact that he was present and could see me play, greet me and give me some words of encouragement was pretty cool," Hovland told Reuters of 83-year-old Nicklas, one of golf's greatest with 18 major victories and 73 PGA Tour victories.
"Shaking my hands a little"
McCarthy had missed a par putt by a few millimeters on the 18th hole that opened the playoff and Hovland sank his putt for par and was able to win the event.
"My hands were shaking a little. These greens are not completely green, but have turned quite brown," Hovland said after his fourth PGA Tour victory. He lifted from seventh to fifth place in the world rankings.
Hovland won at -7. Alex Noren played all four rounds and finished 52nd. David Lingmerth missed the cut and was 89th.