The Boston Celtics had their full roster for the start of their game against the Chicago Bulls on Friday night. It didn’t end that way, but they relied on their sixth man late in the game to pull out a win.

Payton Pritchard scored 19 of his season-high 29 points in the fourth quarter to help Boston rally for a 138-129 win in Chicago.

It was Boston’s seventh straight win and pulls them within a game of Cleveland for the top spot in the Eastern Conference. It also keeps the Celtics in contention for a wild-card spot in the NBA Cup.

Pritchard knocked down seven 3-pointers in his 28 minutes and played the final 19 minutes of the game after Derrick White was sidelined in the third quarter because of a foot injury. Pritchard helped Boston take control midway through the fourth quarter with 11 consecutive points in an 11-4 run to quiet the Chicago crowd.

“It’s obviously a great feeling, but I feel like the best feeling is winning on the road and being able to help my team get over the hump tonight,” Pritchard told reporters in Chicago. “Obviously I feel it. I can hear the crowd, the gravity it pulls. It definitely was a fun night.”

That scoring outburst came with Jayson Tatum (35 points) on the bench. Tatum raved about his 6-foot-1 teammate, who added to his Sixth Man of the Year case.

“I say all the time, me and P, the same high school class, so I’ve been seeing that fearless competitive nature ever since we was like 13,” Tatum told reporters. “It’s been pretty cool to see him grow into the player that he is, being effective on a championship team and the things that he’s doing is Sixth Man of the Year worthy for me.”

The Celtics had six players in double figures and their bench scored 34 points. As his minutes and role grow in his fifth NBA season, Pritchard is appreciative of the respect he’s earned from the Celtics’ veterans and believes that respect stems from one key thing.

“Through the hard work,” Pritchard said. “They see the hours I put in, and that builds respect throughout my teammates. That’s how I get respect from other people, but also how other people earn my respect is through the work.”

That hard work has allowed the late first-round pick to become a crucial part of Boston’s title core. Entering the first year of a four-year contract, Pritchard remains eager to build on the best start of his career.

“Just being confident in yourself, knowing that you belong with the best, and all the hard work and the hours you put in, in the summer time, that you’re capable of coming and helping the team win any given night. I have a strong belief in myself, and I feel like my teammates believe in me too to be able to take that on.”

THE CELTICS HAVE been clear throughout the season: They care about the NBA Cup.

Sure, it’s not the playoffs, but it’s something they can win during the regular season. So with the Celtics fighting to make the knockout stages late against the Bulls, they played hard until the final buzzer in Chicago for point-differential purposes.

The Celtics had a six-point lead with just seconds left, but called a timeout with 1.4 left to get one more opportunity to score. Sam Hauser made a 3-pointer to push the differential to nine. Celtics Coach Joe Mazzulla said postgame he enjoys that aspect of the NBA Cup.

“I like it because this tournament and the point-differential kind of eliminates the unwritten rules that you’re supposed to follow or not follow,” Mazzulla said postgame, via NBC Sports Boston. “Where in a normal situation, you wouldn’t do that. But in this one, you get to draw up a play and try to get better in that situation. So guys did a good job executing and we tried to extend the point-differential as much as we could.”

This is the second straight season the Celtics needed to run up the score on the Bulls. Last year, the Celtics needed to win by at least 23 points, which they did to advance to the knockout stage. This year, the Celtics needed to up their point-differential as much as possible after the Hawks beat the Cavaliers earlier Friday.

The Atlanta win means Boston’s lone path to the knockout stages of the NBA Cup is as a wild card, given to the best second-place team in the three East groups. The tiebreaker comes down to point differential.

Boston finished group play 3-1 to tie Atlanta for first in their group. The Hawks beat the Celtics in their head-to-head matchup, so they win the group.

There are two scenarios that would allow Boston to advance to the knockout stage – the Magic beat the Knicks and the Bucks beat the Pistons by at least five points, or the Magic beat the Knicks and the Pistons beat the Bucks by at least six points.