TAMPA, Fla. — Six games into the season and the Toronto Raptors have, in the words of Fred VanVleet, "a boatload of problems."

"This is probably uncharted territory for most of us," he said Monday night after the Raptors squandered another double-digit lead in falling 126-114 to the Boston Celtics, dropping their record to 1-5.

Pick your poison when it comes to Toronto's shortcomings so far this season. Erratic play, poor defence, subpar rebounding, questions about the bench. And perhaps worst of all, lack of fight.

"We just need to get a little bit more grittier, get a little bit more tougher and a little bit more nastier, and have a little bit of a swag(ger) to us," said a subdued Kyle Lowry.

"Right now we have no swag(ger) to us. Right now we have nothing. There's nothing to us. Teams are looking at us like 'All right, let's go eat.' And that's not a good feeling."

Jayson Tatum scored 40 points as the Celtics, rallying from a first-half deficit, piled on Toronto's early-season misery. The Raptors got off to a hot start with signs that Pascal Siakam might be emerging from his early-season funk. But it turned into merely another blown double-digit lead.

Only the Detroit Pistons (1-6) have a worse record than Toronto.

The Raptors play next at Phoenix on Wednesday, the first leg of a four-game road trip that also includes stops in Sacramento, Golden State and Portland

Toronto's 13-point advantage with a little more than four minutes remaining in the first quarter turned into a 15-point deficit at the half as Boston outscored the Raptors 38-14 in the second quarter for a 61-46 edge.

Tatum led the way with 21 points in a second quarter that saw Toronto make just 5-of-24 shots while missing all six three-point attempts.

The Celtics, who won despite making 20 turnovers to Toronto's 10, led by as many as 23 in the third and were up 100-81 going into the fourth.

A late 11-0 Raptors run cut Boston's lead, once as high as 26 points, to 10 points with less than three minutes remaining, prompting the Celtics to reinsert some of their starters.

Tatum was one off his career high of 41 when he went to the bench early in the fourth. Payton Pritchard, a rookie from Oregon, had 23 points and eight assists off the bench while Jaylen Brown added 19 for Boston (5-3).

Boston's bench outscored the Raptors reserves 60-29. Take away Terence Davis's 4-of-8 shooting and the Toronto bench made 4-of-21 shots.

Coach Nick Nurse was blunt in his takeaway from the night.

"Tonight I didn't learn anything. I didn't learn anything other than we've got to compete harder," Nurse said.

"Hopefully this is not who we're going to be, because we have fought really hard in four of the first five (games). But we just didn't fight hard enough tonight in the middle of the game."

VanVleet led the Raptors with 35 points, one off his career high. Siakam finished with 22 while Lowry added 18.

VanVleet made 13-of-20 shots. The rest of the Raptors were a combined 23-of-70.

"It's a long season, man," VanVleet said. "We've got to stay confident and keep believing in ourselves and in each other. And we'll work our way out of it."

Prior to the game, Nurse pointed the finger at his team's lack of defence and rebounding, saying both had to improve. They didn't on the night.

Boston had a 56-37 edge in rebounds with VanVleet, listed at six foot one, leading Toronto with eight rebounds.

And Nurse lamented his team's inability to defend or ratchet up the degree of difficulty of Boston's shots.

"It's on everybody, myself included, that we're not guarding … It's not any one person in particular. It seems to be spreading," he added.

It was the first meeting between the two since Sept. 11 when the Celtics defeated Toronto 92-87, eliminating the Raptors in Game 7 of their Eastern Conference semifinal. Monday also represented Toronto's third regular-season game at Amalie Arena, the Raptors' home away from home during the pandemic.

Boston was missing two key players in the injured Kemba Walker (knee) and Marcus Smart (thumb).

The Celtics, who edged the Pistons on Sunday on a late Tatum basket to complete a split of their two-game series in Detroit, have now won four of their last five games. Toronto was coming off a 120-116 loss in New Orleans on Saturday.

Boston was also without Jeff Teague (ankle), Romeo Langford (wrist) and Javonte Green (health and safety protocols).

Hitting five of their first six three-point attempts, including two by Siakam, the Raptors built an early 17-5 advantage and led by as many as 13 before ending the quarter up 32-23.

Boston scored the first bucket and then fell behind as Toronto made 7-of-14 three-pointers in the first quarter and had 11 free-throw attempts, albeit missing six. VanVleet sank four of those three-pointers in his 14-point opening quarter.

Toronto went cold and Boston tied it at 36-36 on a 10-0 run, with the Celtics continuing to pull ahead. And the Raptors ship continued to tip in the second half.

Siakam showed his skills with a one-handed dunk midway through the third quarter.

Siakam, who fouled out of his last two appearances, came into the contest averaging 16.5 points a game on 39.4 percent shooting. He averaged 22.9 points a game last season on 45.3 percent shooting.

Toronto's worst start to the season was an 0-9 run in 2005-06, a campaign that saw Chris Paul named rookie of the year and Canada's Steve Nash crowned MVP. The Raptors ended the season 12th in the East at 27-55.

This report by The Canadian Press was first published Jan. 4, 2021