Josh Smith scored 20 points for the Rockets, who trailed 89-88 at the end of the third quarter after Phoenix rallied from an early 18-point deficit.
Eric Bledsoe scored 32 points, one shy of his career high, for the Suns, who enter the All-Star break losers of five of their last six.
Harden ended the first and second quarters with a three-point basket, then opened the fourth with a four-point play that put the Rockets ahead for good. He scored eight in a row during a 2 1/2-minute stretch late in the game.
Harden scored 45 in a loss to Portland on Sunday and has six games of 40-plus points. Houston won for the seventh time in nine games.
at Memphis 95, Brooklyn 86:
at Chicago 104, Sacramento 86: