Fred VanVleet admitted his costly turnover was the "turning point" as the Toronto Raptors fell to a 128-122 defeat to the Portland Trail Blazers.

Starting in place of All-Star Kyle Lowry, who sat out due to a thigh contusion, VanVleet impressed during close to 38 minutes on the floor with a season-high 21 points and eight assists.

However, the third-year point guard lost possession when forcing a fast break, allowing CJ McCollum to sink a three-pointer and put the Blazers up by five with one minute and 16 seconds remaining.

Toronto took a timeout but committed a five-second violation when they failed to inbound the ball to restart the action, with Al-Farouq Aminu scoring from beyond the arc on the next play to put Portland truly out of reach.

"It is what it is and hindsight is always 20-20. I go in there and get an and-one, get a layup, I'm a hero, it's a tie game," said VanVleet.

"The ball gets stripped there and I suck, I'm stupid and if Kyle plays we win the game. You know what I'm saying? You've got to live with that. I'm gonna make mistakes. I'm gonna play as hard as I can … that was obviously a turning point there."

Although they were without Lowry, Kawhi Leonard returned for the Raptors after missing two matches with a thigh complaint.

VanVleet admitted Toronto, who lost Pascal Siakam in the second quarter to a back problem, are still getting used to working the two-time Defensive Player of the Year into their offense.

"Obviously you've got a talent like that you probably try to cater to them a little bit and he's probably going to have to do a good job of catering to what we do as well," said VanVleet.

"It's trying to find that balance, man. We have to plug him in and see where we think he can fit. You saw how the offense moves without him, it's just a matter of figuring out how to find a happy medium.

"He's kind of giving in a little bit and we're giving in a little bit and we'll find ourselves in the middle there, but it will take some time."

Raptors coach Nick Nurse highlighted the impact of Portland's bench, which accounted for a huge 58 points.

"They really played great, right from the start they were super fast, cutting hard, making shots and making the right decisions. I thought we were a half-step slow out of the gate," said Nurse.

"Their bench was unbelievable … they just put it on us. We got it right where we needed to start the fourth and then it was like a one-minute barrage. We had to climb back up the hill again and we almost did it."