Valanciunas had 17 points while Amir Johnson added 16 points as Toronto earned a 109-102 home win over the Atlanta Hawks on Wednesday night.
DeRozan had 15 points but finished 4 for 16 from the field and 0 for 1 from three-point range. Lowry, who signed a new four-year, US$48-million deal this summer, scored 11 points but made 3-of-11 shots and missed his three three-pointers. But the pair found other ways to contribute as DeRozan recorded career highs in rebounds (11) and steals (six) while Lowry added 10 assists.
"I'm not just trying to be a scorer," DeRozan said. "If we're not making shots we all have to figure out ways we can affect the game in a good way.
"I think the first one is always the toughest . . . you want to get that win out of the way."
Toronto shot 41 per cent from the field but made 27-of-33 free throws, outrebounded Atlanta 48-40 and had 26 assists with just nine turnovers .The Hawks shot 50 per cent and 59.1 per cent from three-point range (13 of 22) but committed 19 turnovers that led to 23 Raptors points.
"There's other ways to win other than looking at the shooting stats," Toronto head coach Dwane Casey said. "We had 26 assists and only nine turnovers and that was huge for us . . . we got to the free-throw line and out-rebounded them."
Added Lowry: "We are a team, we are a complete team. DeMar and I didn't play that well offensively but we did other things to help the team win.
"Greivis (Vasquez) played well, the big fella (Valanciunas), Amir played well and everyone filled up a role."
Johnson eclipsed his previous opening-night high of 13 points for Toronto, which improved to 11-9 all-time on opening night and 8-6 when starting the season at home. That delighted the loud, enthusiastic Air Canada Centre sellout of 19,800, many donning the free white We The North t-shirts left on their seats as they arrived.
"The crowd was really good, it reminded me of the playoffs," said Valanciunas, who was 4 for 5 from the field and made 9 of 10 free throws. "They were standing, cheering for us, that was great."
Terrence Ross added 13 points for Toronto, now 12-8 all-time in home openers while Williams added eight points against his former team. The Raptors acquired Williams and Lucas Nogueira from Atlanta on June 30 for John Salmons.
Kyle Korver, Jeff Teague and Mike Scott all had a game-high 20 points for Atlanta.
The Raptors are coming off a club-record 48 wins last year that earned them their first playoff appearance since 2008. But Toronto's promising season ended with a heart-breaking seven-game opening-round loss to the Brooklyn Nets.
Toronto will face teams that qualified for last year's playoffs in four of its first six games. The good news is the Raptors will play nine of their first 12 contests at the ACC, where they were 26-15 last season.
Toronto was 2-2 last year with Atlanta, which claimed the eighth Eastern Conference playoff seed last year with a 38-44 record. The Hawks' season also ended bitterly with a 4-3 opening-round playoff loss to the Indiana Pacers.
But it was an anxious finish for Toronto, which led 90-71 early in the fourth on consecutive baskets from Valanciunas. However Scott's three-pointer pulled Atlanta to within 103-99 with 1:26 remaining before two Lowry free throws boosted the Raptors' lead to 104-99 with 46.8 seconds left to play.
A goaltending call on Patrick Patterson allowed Atlanta to make it a four-point game (105-101) before two DeRozan free throws increased Toronto's lead to 107-101 with 32.4 seconds to play. Teague made one-of-two free throws to make it 107-102 but Patterson's dunk with about 13 seconds remaining cemented the victory.
"It wasn't like we were slacking," Casey said. "A couple of times in transition we lost them but a lot of times they made shots.
"Sometimes you have to tip your hat to a team that's shooting that well."
Hawks coach Mike Budenholzer credited his team for rallying from the 19-point deficit in the fourth.
"I felt good about our guys fighting back," he said. "We have to take care of the ball.
"Our turnovers led to a few of their runs so if we can take care of the ball better I think that will help us. They were a little bit more physical, a little bit more active than us for more of the game."
Williams' buzzer-beater put Toronto ahead 86-71 at the end of the third after the Raptors outscored their visitors 26-19 in the quarter.
Toronto led 60-52 at the half as three-pointers from Ross and Patterson anchored a 9-2 run to finish the half. The Raptors had extended their lead to 38-28 earlier in the quarter but following three three-pointers from Korver, Atlanta pulled to within 51-50 on five straight points from Teague, including a three-pointer with 2:23 remaining.
Al Horford's basket in the dying seconds cut Toronto's lead to 24-22 after the first. Atlanta led just once in the quarter, 3-2 on Korver's early three-pointer before the Raptors went on a 9-2 run to regain the advantage with Johnson and DeRozan scoring six points apiece.
NOTES — Casey appeared in his fourth opening-night game for Toronto . . . This marks the first time Toronto and Atlanta have met on opening night . . . As part of the Raptors' 20th anniversary, the team will sear a special patch on its home white jersey . . . Centre Greg Stiemsma (sprained ankle) was out for Toronto . . . While Toronto posted a 7-1 exhibition record, Atlanta was 4-3 . . . In Toronto's four games versus Atlanta last year, DeRozan was the Raptors' leading scorer three times. Lowry was the top point-getter in the other . . . Toronto visits the Orlando Magic on Saturday night.