The Nuggets led by five early in the fourth. The Clippers scored eight straight points, including five by Wesley Johnson, to go up 90-87.
Neither team led by more than seven points the rest of the game.
Clinging to a 99-98 lead, Harrell missed a pair of free throws, shaking his head as he backed away from the line. He got fouled twice more in succession and made 3 of 4, extending the lead to 102-98.
Harrell came up with a block on Plumlee at the other end, and Johnson hit a 3-pointer, making it 105-98.
Denver got to 106-104 on four straight points by Harris and two free throws from Barton.
The Nuggets ran off 11 straight points for a 79-69 lead in the third only to blow all of it. The Clippers answered with their own 11-0 spurt, including consecutive 3-pointers by Tyrone Wallace and Harrell, to lead 80-79. Emmanuel Mudiay's basket sent Denver into the fourth leading 81-80.
Nuggets: They are 8-14 against the Clippers at Staples Center over the last 11 seasons. ... Denver fell to 7-17 on the road overall and 3-13 against the West away from home.
Clippers: C DeAndre Jordan (sprained left ankle) missed his third straight game and the swelling hasn't gone down. Jordan had initially been expected back Saturday in Utah, but coach Doc Rivers says he's not ready and won't be rushed. ... G Austin Rivers (right ankle) has missed eight straight games. He is wearing a boot and will be re-evaluated in the next week.
Nuggets: Host Phoenix on Friday, having beaten the Suns by 23 on Jan. 3.