Duncan scored 20 points and had 10 rebounds on Friday night as the Spurs beat the Celtics for the 17th straight time, 101-89.
Boston is the only team in the NBA without a victory over San Antonio during the Duncan era, though it had some chances Friday when the Spurs surrendered several double-digit leads.
"We played well for the majority of the time," Duncan said. "We had a little bit of ups and downs -- a little more than we wanted to."
San Antonio led by as many as 16 in the third quarter, but the Celtics trimmed that to 75-65 at the end of the period.
Boston's Orien Greene scored on a fast-break layup to make it 79-71 with about 10 minutes remaining. But Duncan then made a left-handed jumper and Nick Van Exel found Manu Ginobili for an alley-oop layup, and after that the Celtics never got closer than 10.
"I thought we caught the Spurs on an off night," Boston coach Doc Rivers said. "They were beatable."
But the last time the Celtics did beat San Antonio was in January 1997, five months before Duncan was drafted first overall by the Spurs. The Celtics finished with the NBA's worst record during the 1996-97 season and had the best shot at Duncan, but they ended up getting Chauncey Billups with the third pick.
"They're a well-oiled machine -- they've been together for a long time and they understand what it takes to win," said Paul Pierce, who led Boston with 24 points after shooting 3-for-9 in the first half. "They withstand runs, they don't get rattled. ... They are definitely a team we can learn from."
The Spurs had a season-high 11 blocked shots, six by Rasho Nesterovic and the other five by Duncan.
"The blocked shots are the consequence of our defensive system," Ginobili said. "We were trying to make some of [the Celtics] penetrate and we always want the bigs to defend them."
Ginobili grabbed the opening tip and drove for a reverse layup and then added two more baskets as the Spurs took a 10-2 lead. He also had three steals in the first period.
Boston battled back but San Antonio used a 9-2 run, capped by a pair of free throws by Ginobili, to go up 19-10 late in the period.
A short jumper by Delonte West trimmed the Spurs' lead to 39-33 with about five minutes left in the half, but San Antonio went on a 10-2 spurt to build their largest advantage of the first half at 49-35.
The Celtics narrowed the difference to 51-42 at the break on a layup by West that just beat the buzzer.
The Celtics have lost 16 straight games in San Antonio. The last Boston victory here came in February 1990. ... Finley made San Antonio's 100th 3-pointer of the season midway through the fourth quarter. ... San Antonio is 15-0 when leading after three quarters. ... Boston is 0-5 in the first game of a back-to-back series and 1-3 in the second game. The Celtics play Saturday night in Dallas. ... Boston scored baskets at the buzzer in each of the first three quarters.