Jaylen Brown said he meditated twice a day during his COVID quarantine. It looks like it helped his game

Jaylen Brown drives to the basket in the second half of Wednesday's loss to the Knicks.Frank Franklin II/Associated Press

NEW YORK — Celtics forward Jaylen Brown returned for Wednesday’s opener against the Knicks after being sidelined for nearly two weeks because of a COVID-19 diagnosis. Brown said he was mostly asymptomatic but dealt with some breathing issues while he was quarantined.

“I had to really focus to get my breathing kind of back to normal,” he said. “That was kind of the most concerning thing to me. But the more I focused on it, the better I was able to gain more efficiency in it. But, for the most part, mild symptoms. Nothing too concerning.”

Brown took part in four-on-four scrimmages and shooting drills at the Celtics’ practice on Tuesday. He said the team will have an inhaler available for him during games, but he hopes it is not needed. During his quarantine period he meditated twice a day, in large part so he could focus on his breathing.

“If my breathing is altered,” Brown said, “my life is altered.”

Brown scored 25 first-half points — including 20 in the first quarter — to help the Celtics take a 58-54 halftime lead over the Knicks. He finished with a breathtaking 46 points in 46 minutes, hitting 16 of 30 shots, including 8 of 14 from 3-point range in a 138-134 double-overtime loss.

Celtics forward Al Horford, who tested positive for COVID-19 on Oct. 11, remained sidelined on Wednesday night. Coach Ime Udoka said that Horford is “feeling good” and that the Celtics are hopeful that he will be able to return soon.

Players are required to quarantine for 10 days after a positive test, and then must produce two negatives tests before being cleared. That timeline would give Horford a chance to play against the Raptors at TD Garden on Friday night.

Third-year forward Grant Williams started in place of Horford against New York.

Ime Udoka talks to Dennis Schroder during the first overtime of Wednesday game.Frank Franklin II/Associated Press

“He’s been consistent,” Udoka said of Williams. “He’s very versatile. He covers a lot of different areas for us, can guard bigs and smalls, and is a guy that has been here. With him, it’s a matter of being consistent. He showed us that this preseason and in training camp, and with Al out, he’s a guy that does a lot of similar things.”

Guard Josh Richardson sat out on Wednesday because of a migraine. Point guard Payton Pritchard, who broke his nose in Boston’s preseason loss to the Magic last Wednesday, was cleared to return with a mask.

Brown: Kemba ‘like an older brother’

Brown said all of the Celtics were surprised last summer when point guard Kemba Walker was traded to the Thunder. He later reached a buyout agreement with Oklahoma City and signed with the Knicks.

“Obviously, what the front office does is what the front office does, but it was such a joy having Kemba around,” Brown said. “For me, he was one of the people I drew inspiration from. Things I learned when Kemba was here, I added to my game.

“He was always somebody who, despite circumstances, despite however I felt, he was always somebody that was just like, ‘Be patient, you’re fine, your time is coming.’ He was always that person in my ear giving me motivation. He was always that person who was trying to put a smile on my face, telling me, like, ‘It’s not that serious,’ making jokes, because I can get pretty intense.”

Walker played for the Celtics for two seasons, but lingering left knee issues held him back a bit. He did not play in games on back-to-back nights last year, and he missed the final two games of the Celtics’ opening-round playoff loss to the Nets. But he always had the support of his teammates such as Brown.

“Kemba was a great guy and a great friend to me, like an older brother,” Brown said. “So, I definitely miss him. I miss his energy around.”