Karlsson, acquired by San Jose in a trade with the Ottawa Senators on Sept. 13, had 45 points (three goals, 42 assists) in 53 regular-season games and was tied for second on the Sharks with 16 points (two goals, 14 assists) in 19 Stanley Cup Playoff games. But he played through a groin injury for much of the second half of the season and could not play when San Jose was eliminated by the St. Louis Blues in Game 6 of the Western Conference Final on May 21. He had groin surgery 10 days later.
With Karlsson expected to be healthy for the start of next season, DeBoer believes the 29-year-old will be an impact player for the Sharks.
"He played two, two and a half months in January-February where he controlled the game every game," DeBoer said. "He was our best player almost every night and then he got hurt. So we saw enough during that period that we were very comfortable."
Having a defense corps anchored by Karlsson, Brent Burns and Marc-Edouard Vlasic has DeBoer feeling good about the San Jose's chances to remain Stanley Cup contenders after they finished 46-27-9 this season, second in the Pacific Division to the Calgary Flames.
"It gives us a chance to win," DeBoer said. "You have those guys in the lineup, especially at a key position, it gives you a legitimate chance to win every night if they're healthy."
Thornton's return will help, too. After spending each of the past two off-seasons working his way back from knee injuries -- he tore the ACL and MCL in his left knee in 2017 and tore the MCL in his right knee in 2018 -- Thornton had a strong 2018-19 season, with 51 points (16 goals, 35 assists), averaging 15:33 in ice time in 73 games.