The New York Knicks claimed their ninth straight win on Sunday but top scorer Immanuel Quickley says they are not satisfied.

The Knicks improved their record to 39-27, firming up fifth spot in the Eastern Conference with Sunday's 131-129 double overtime win over the Boston Celtics fuelling the hype surrounding the side.

Quickley stepped into the starting line-up for the absent Jalen Brunson, who was the Eastern Conference Player of the Month for February, before scoring a career-high 38 points showcasing the Knicks' depth.

"We're not satisfied at all," Quickley told ESPN. "We want to continue to get better. We want to continue to make a push down the stretch."

The Knicks are firmly in contention for one of the top four seeds in the East, which would earn them home-court advantage in the first-round of the playoffs.

The Milwaukee Bucks (46-18) and Celtics (45-20) are well out in front in, but the Knicks are closing in on the third-placed Philadelphia 76ers (41-22) and fourth-placed Cleveland Cavaliers (40-26).

Quickley's performance, across a career-high 55 minutes, included making five-of-12 from three-point range with eight rebounds and seven assists, though he was not interested in individual accolades.

"My team-mates did a great job," he said. "I'm really proud of my team. Double overtime against a really good team. You can't ask for better."

The defeat dealt another blow to the Celtics, who have dropped three of their past four games, including two against the Knicks.

Boston had led by 14 points, having allowed the biggest comeback of the season on Friday when the Brooklyn Nets rallied back from 28 points down.

"We're not locking in as much as we need to," said Celtics veteran Al Horford, who missed an attempt for a game-winning three-pointer on the second overtime buzzer.

"This is the second time we've had a lead, we feel good about it and a team makes a run and we let them back in the game.

"Throughout the season you're going to have adversity. We've played pretty good basketball most of the year. This is a time when you tighten up and fix some of these issues or it goes the other way.

"We want to play our best basketball, but this is a part of the season. There's ups and downs."

Celtics guard Derrick White claimed they have lost their "swagger", having surrendered top spot to the Bucks over the past week.

"We've just got to get our swagger back," White said. "Find a way to play with each other, have fun out there. I'm sure we'll get it back here soon."