BOSTON — Isaiah Thomas said he didn’t feel any pressure entering the first Game 7 of his career.

His play backed up his confidence and with the help of Kelly Olynyk and the Boston Celtics bench, Thomas earned the biggest win of his career.

Thomas scored 29 points and had 12 assists, Olynyk scored a career-playoff high 26 points and the Celtics used a big fourth quarter to outlast the Washington Wizards 115-105 in Game 7 of the Eastern Conference semifinals Monday night.

“I knew it would be a big time game tonight. I knew it wouldn’t be easy at all,” Thomas said. “And we came out on top.”

Led by Olynyk the Celtics got a huge lift from their bench, outscoring their Wizards’ counterparts 48-5. Boston also connected on 11 3-pointers, including 8 of 13 in the second half.

“We needed it,” Olynyk said. “That’s a tough team that we played seven tough games against and they can score. We needed to help out the starters, help out Isaiah.”

Boston advances to the Eastern Conference finals, where it will host the Cleveland Cavaliers in Game 1 on Wednesday. It’s the Celtics first appearance in the conference finals since 2012.

“What a special opportunity to get a chance to compete against them,” Boston coach Brad Stevens said.

For Thomas it serves as the ultimate validation for a team that many felt was unworthy of the conference’s top seed. It also marked the latest big performance by Thomas, in a playoff run that began in the haze of his younger sister’s death in a car accident. The 28-year-old All-Star has called the basketball court his sanctuary.