Knicks guard Jalen Brunson drives past Suns center Bismack Biyombo, center,...

Knicks guard Jalen Brunson drives past Suns center Bismack Biyombo, center, and forward Mikal Bridges, left, during the first half of an NBA game in Phoenix on Sunday. Credit: AP/Ross D. Franklin

PHOENIX — When the Knicks lost at Golden State on Friday night, they bemoaned the slow start that had put them in a hole, insisting that the lesson was that they needed to be ready from the start and play for four quarters.

The ready-to-start part was in effect Sunday afternoon. The play-for-four-quarters request was not. 

The Knicks trailed by two at halftime against the Suns but collapsed under a downpour of three-point field goals, falling behind by as many as 26 points in the fourth quarter and dropping a 116-95 decision at Footprint Center. 

Tom Thibodeau waved the white flag midway through the fourth quarter, emptying the bench with the final stop of a five-games-in-seven-nights trip awaiting them Monday night in Oklahoma City.

“I thought we played well in the first half,” Thibodeau said. “But against a team like this, you have to play well for all four quarters, 48 minutes. So we had that lull. You give a team like that a second and third crack at things, they’ll make you pay for it, and they did.”

The Knicks  were without Cam Reddish, who suffered a strained groin Friday, and inserted Quentin Grimes into the starting lineup. Grimes had 10 points and a career-high eight assists in 32:11, playing respectable defense and drawing tough assignments. But even with the Suns playing shorthanded without Chris Paul and Cam Johnson, it was not nearly enough.

Jalen Brunson provided a burst in the third quarter and led the Knicks (8-9) with 27 points, but Julius Randle was limited to  nine points and RJ Barrett again struggled offensively, scoring 12 points and shooting 3-for-11.

Barrett’s continuing shooting problem — he is 20-for-76 overall and 2-for-25 from beyond the arc in the last five games — has taken away one of the weapons that normally might help the Knicks out in a game like this. 

While he has spoken of getting to the rim for a few easy baskets to get going, Barrett had just two field-goal attempts in the first quarter — both from three-point range and both misses.

“The big thing is a couple of easy baskets can get him going,” Thibodeau said. “Whether it’s moving off the ball, screening, cutting, slipping, running the floor. Oftentimes you go through ups and downs in this game. Just work your way through it. Hustle plays. Oftentimes a couple hustle plays, a couple of easy baskets, you start feeling good and it’s a big difference. Just keep working.”

“Just trying to take the shots the game is presenting and be aggressive with it,” Barrett said. "So very confident and that’s how I got to keep approaching it.

“You want to take the smart ones, the easy ones, so you see the ball go in. But I’ve also seen the other way when you have a really good stretch for however many games. So it’s the ups and downs. My goal is to play consistently and I have to get to that.”

In those five games, he  not only has struggled to make shots but has taken as many as anyone on the team. His 76 have been matched by Brunson and are more than Randle’s 72.

“Good and bad, you have to stay positive,” Brunson said. “He works really hard. So it’s not for a lack of work or anything like that. It’s all mental at this point. We all have slumps. We all shoot sometimes the way you don’t want to. But it’s all about staying mentally strong, and he’s a guy who is mentally strong.”

Cam Payne, starting in place of Paul, led Phoenix (10-6) with 21 points, nine assists and seven rebounds. Devin Booker added 20 points and the Suns had six players in double figures. 

The Knicks trailed by only 64-62 four minutes into the second half but fell behind by as many as 17 as the Suns began to connect from beyond the arc, draining three straight at one point. Phoenix brought a 90-75 lead into the fourth quarter.