"We thought it was going to be a cake walk," Wallace said.
Loren Woods had 17 points and a career-high 14 rebounds and
Vince Carter scored seven of 12 points in the final three minutes to help the Raptors improve to 2-0 with a 101-89 victory over the Detroit Pistons on Friday night.
The Pistons were without coach Larry Brown, who had surgery on his left hip Wednesday and is expected to be away from the team for seven to 10 days.
"It was our defense that hurt us," said Gar Heard, who is running the team during Brown's absence. "We gave up so many easy layups, so many uncontested shots, so many second shots."
Detroit gave up 100 or more points for the first time since Feb. 7, 2004 at Dallas -- a span of 31 regular-season games.
Chris Bosh led a balanced Toronto attack with 18 points, as six Raptors players reached double figures.
Toronto's reserves outscored Detroit's backups 30-8. The Pistons' reserves scored only six points in their season-opening win on Tuesday.
"They are still probably enjoying a little bit of the championship, so we have to figure out a way to get some effort off the bench," Heard said.
Woods, Toronto's new starting center, recorded his first career double-double and came within one point matching his career high.
Woods was also impressive in Toronto's season-opening victory against Houston on Wednesday, holding Yao Ming to 17 points.
"I haven't been on a roll like this since I've been in the league," said Woods, who is on his third team in four years.
After Rafer Alston's 3-pointer from the corner gave Toronto a 10-point lead with 4:19 left, Carter blocked Hamilton's shot and Woods followed with a fast-break layup.
Carter's fadeaway jumper gave Toronto 94-80 lead with 3:01 remaining.
After Wallace's dunk attempt rattled off the back of the rim, Carter knocked the ball down the court with his fist to Woods, who made a tip-in.
Carter followed with a 3-pointer and a jumper, giving Toronto a 101-85 lead with 1:34 left.
"It's a great win, especially for a team that's been counted out before we played our first game," Carter said.
Toronto held a 49-47 lead at the half. Detroit led by 10 after one quarter, but Morris Peterson's four-point play highlighted a strong second period in which the Raptors outscored the Pistons 28-16.
Heard, 64, coached Dallas in 1993 and Washington in 2000. ... Attendance in Toronto was just 15,284 for the defending NBA champions. ... Peterson has three four-point plays in his career. ... Jalen Rose, who is from Detroit, saw his only Pistons game after his high school team won the state championship. Rose and his teammates were allowed into the Detroit locker room after Larry Bird and the Boston Celtics blew out Detroit. "We walked in and Bill Laimbeer was like, 'Get those kids out of here," he said. "So we waited by the Celtics' bus and shook their hands."