This 107-97 loss was embarrassing considering Toronto was missing an All-Star and integrating two new players — Serge Ibaka and P.J. Tucker — into their system. Still, they are in the Celtics’ heads. They own Boston for now — winning the season series, 3-1 — and the Celtics have two months to rectify that.

The Celtics were ahead by 17 points late in the second quarter Friday at Air Canada Centre, only to fold to the Kyle Lowry-less Raptors, getting outscored by 20 points after halftime.

What was even more demoralizing was the performance or inactivity of maximum-contract power forward Al Horford, who attempted five field goals in 30 minutes and finished with 8 points and five rebounds. On a night when the Raptors were squeezing Isaiah Thomas like a lemon, sending three defenders at him or inviting him to penetrate only to be gobbled up by two big men, Horford was rather passive.

That’s primarily because his teammates were jacking up 3-pointers — 26 missed 3-pointers in 38 attempts, including a combined 4 for 17 by Thomas and Marcus Smart. The Celtics become 3-point crazy at times, leaving Horford to roam the perimeter. The offense relies on ball movement and perimeter shooting, but when Horford is 22 feet away from the basket, he can’t be effective in the paint or rebound.


So it’s about time the offense begins to feature him as defenses continue to blitz Thomas, who was 6-for-17 shooting and 1-for-6 with just 4 points in the fourth period.

Horford took one shot in the final period, making a short jumper, but pulling down no rebounds. Horford is a flow player, meaning he won’t put his imprint on the game unless his teammates get him involved. He needs to get involved in games earlier, get some easy buckets and make defenses shift, thus opening opportunities for Thomas.


Honestly, why in the world would any defense single-cover Thomas in the fourth quarter when it knows Horford is going to take one or two shots? Without Avery Bradley in the lineup, the Celtics desperately need a secondary scorer. They have a few, and Horford, when he is engaged, is one of them.

He is not without fault. Horford has to demand the ball, growl at Thomas when he’s open. He needs to rebound better, get putbacks, get to the free throw line. He attempted two free throws Friday and has attempted just 90 in 46 games this season, fewer than two per game.

Horford has never been a volume free throw shooter, but he has attempted only three more than Jaylen Brown in more than 650 more minutes.

Since president of basketball operations Danny Ainge placed confidence in this roster by leaving it intact through the trade deadline, coach Brad Stevens has to devise a way to get Horford more involved.

“Definitely, we’ve got to [get Horford more involved] and that’s my job,” Thomas said. “I’ll do a better job of getting him the ball Sunday [against Detroit] and making sure he’s in the flow of the game and not just defensively, but offensively as well.

“We’ve got to get him the ball. He’s a key factor what we do and our success.”

When asked if he needs more than five shot attempts, Horford said, “I think so. I think the way they were playing us, they definitely made it hard for me to get any looks. But yeah, there’s no question.”


Horford has been the consummate teammate but now it’s time to be more demanding and more responsible for the fate of this team. This was the seventh game this season Horford has scored in single digits and the 40th (of 46) that he has collected fewer than 10 rebounds.

The Celtics need toughness, but yet watched as Toronto acquired the attainable Tucker, who finished with 9 points and 10 rebounds in 29 minutes. So this roster has to respond with more passion and execution, especially Horford, who needs to find a way to impact every game, and Friday he made no impact.

“I gotta see the flow of the game, I got to get him the ball, there’s no excuse for it,” Thomas said of Horford. “I’m the point guard of this team and I’ve got to do a better job of getting him the ball in his spots. He has to do a good job of getting open and demanding the ball, but I’ll do a better job of that on Sunday.”

The pressure is on. Toronto added to key pieces. Washington and Atlanta added shooters. The Celtics have so far stood pat.

For now, let’s assume this is the Celtics. Friday was demoralizing considering they actually led this game by 17 with 1:29 left in the first and lost the lead 7:31 later. Toronto punched Boston in the mouth, shut down Thomas with stellar defense and his teammates couldn’t respond to rescue him — especially Horford.


And Horford and his teammates are to blame. He has to stop being the nice guy and his teammates have to realize that he is a four-time All-Star and start allowing him to make plays. There is no excuse for what happened Friday. The Celtics need to realize they are the hunted and can be caught by their reinvigorated rivals.

Gary Washburn can be reached at gwashburn@globe.com. Follow him on Twitter @GwashburnGlobe.