He scored five times during a four-game goal streak in Games 4-7 of the Cup Final, becoming the first player to score in four straight Cup Final games since Wayne Gretzky had seven goals for the Edmonton Oilers in Games 2-5 against the Philadelphia Flyers in 1985.
O'Reilly scored two goals in Game 4, including the game-winner in a 4-2 victory. He scored the first goal in Game 5, a 2-1 win. He had the only Blues goal in a 5-1 loss in Game 6. He scored the first goal in Game 7.
He ended the series on a six-game point streak (five goals, four assists), the longest in the Cup Final since Mark Messier had at least one point in six straight for the New York Rangers against the Vancouver Canucks in 1994.
"He's an absolutely stud," Blues center Brayden Schenn said. "He's a beast, all playoffs. Does it in both ends. Selke Trophy] winner, chances are, Conn Smythe winner, Stanley Cup champion all in one year. The guy is an absolute beast."
O'Reilly received 13 of 18 first-place votes from a panel of Professional Hockey Writers' Association members. Blues goalie Jordan Binnington received the other five first-place votes to finish second, and Bruins goalie Tuukka Rask was third.
O'Reilly, who is a finalist for the Selke as the best defensive forward in the NHL, did it while playing with a cracked rib, an injury he sustained in the Western Conference First Round against the Winnipeg Jets, his father, Brian O'Reilly, said.
"He had to really adjust his game," Brian O'Reilly said. "He stayed in it and found a way to do it. They had great people working on him, and it took him a bit to play through the pain and find a different way to do things that he would normally do, which again, he never complained about."
[RELATED: [Stanley Cup Final coverage | Maroon savors winning Cup with hometown Blues]
O'Reilly said the injury was manageable until he got hit in the conference final against the San Jose Sharks. It created a challenge for him on face-offs in particular, but he said his adrenaline took over and he didn't notice the injury.
"That guy is a legend," Blues goalie Jordan Binnington said. "He's an incredible player, an incredible teammate. You can't say enough positive things about him."
O'Reilly came to the Blues from the Sabres, who finished last in the NHL in 2017-18 with 62 points. He took the brunt of the blame and talked about how the losing took away his passion for winning, how he was playing just to get by.
He had 61 points (24 goals, 37 assists) in 81 games.
The trade to St. Louis reignited him. He talked about winning the Stanley Cup in his first conversation with Blues general manager Doug Armstrong following the trade.
"I was so amped up and I said, 'Let's go win a Cup,'" O'Reilly recalled.