Vlasic sustained a concussion and knee injury in the first period of Game 5 against the Kings and missed the rest of the series in 2014.
This year, Vlasic missed the final 12 regular-season games with a knee injury, but skated with Justin Braun, his regular top-pair defensive partner, throughout practice Monday and will be in the lineup for Game 1 on Thursday at Staples Center (10:30 p.m. ET; CNBC, CBC, TVA Sports, CSN-CA).
"I'm looking forward to playing," Vlasic said. "Took the time to heal properly and now I'm ready to go."
The Sharks went 7-5-0 without Vlasic in their final 12 games.
"I think the addition of the depth throughout the year has made it easier for us to handle absences like his," DeBoer said. "But you don't replace a world-class defenseman like that. It's nice to have him back."
Forward Matt Nieto (broken knuckle) also missed the final 12 regular-season games, but practiced Monday and will return for Game 1. Nieto, one of San Jose's fastest skaters, was on the third line with center Patrick Marleau and Melker Karlsson.
"I feel great, 100 percent," Nieto said. "I'm ready to go. Everything's fine. Shooting the puck, fine. There's not a situation that I'm iffy about right now. I wouldn't come back if I weren't 100 percent. I'm feeling really good."
The Sharks went 3-1-1 against the Kings this season, winning each game at Staples Center and one of three in San Jose.
"I think every game we play them is intense," Thornton said. "It's no secret both teams don't like each other. Every game we play against the Kings both buildings are electric, both buildings are tough to play in. They're just fantastic games to be a part of."