On Monday night, James Harden smashed his previous scoring high as a Sixer and startled the Celtics.
Boston came out swinging in Game 1 of their second-round series against the Philadelphia 76ers at TD Garden, hitting 17 of their first 20 shots and taking a double-digit lead at the intermission.
But the Sixers hung in there, getting timely buckets from James Harden and capitalising on Celtics turnovers to erase the deficit and tie the game heading into the fourth quarter.
That's when Harden took over, scoring 15 of his game-high 45 points in the fourth quarter to lead Philadelphia to a 119-115 victory on the road.
Not only was the loss demoralising for a Celtics squad that came in as 10.5-point favourites, but it was also the first of its sort in the shot clock era.
Boston is the first team in NBA history to lose despite shooting 55 percent or better (58.7 percent) and committing 10 or fewer fouls.
Although the Celtics' 16 errors didn't help their situation, Boston's defence, especially its strategy for containing Harden, was the main culprit.
The Celtics tried switching on Harden in the first half and periodically threw double-teams at the Sixers star to try to disturb his rhythm. Harden, on the other hand, made Boston pay.
Harden had four assists in the first two quarters, including two to DeAnthony Melton, who made 5-of-5 3-pointers in the first half, while scoring 21 points.
The C's used more one-on-one coverage in the second half, and Harden reacted by taking over offensively.
The 33-year-old scored 15 of Philadelphia's 32 points in the fourth quarter, including a game-winning 3-pointer over Al Horford in single coverage.