Harden scored 32 points as the Rockets prevailed 114-106 to improve their season record to 4-3.
Harden scored 32 points -- including 14 in the final quarter -- as the Rockets prevailed 114-106 to improve their season record to 4-3.
Harden's final quarter points spree rescued the Rockets, who had trailed 95-94 with just over seven minutes remaining in the game.
However Houston pulled away with a run of 12 points to lead 106-95 with 3:43 remaining.
Ryan Anderson chipped in with 23 points while Trevor Ariza added 15 points.
But D'Antoni was alarmed by the way his team had shipped points in the first and third quarters, conceding 30 and 36 points respectively.
"We had two really good defensive quarters and two really bad ones," D'Antoni told reporters.
"We've got to smooth it out and keep working on it. We did enough to win. It wasn't pretty, but we'll take it."
Nevertheless, D'Antoni is confident his team has the savvy to improve their defense.
"We're not even close to where we need to be as a team," he said. "But that's good because we've got room for improvement and there's no reason why we can't keep improving."
Harden meanwhile also backed the Rockets to tighten up their defensive game, as they managed to do in the decisive fourth quarter.
"That was the only way we'd have the opportunity to win, through our defense," Harden said.
"First quarter we gave up 30 points, second quarter we gave up 17. We were just too inconsistent.
"But fourth quarter we did a great job of blocking in and playing harder. We'll figure it out.
"We are going to make mistakes but we are going to have each other's backs."
The Rockets made 17 of 37 three-pointers and shot 51.9 percent from the field.
Both Anderson and Ariza sank three-pointers in the decisive stretch of the match.
For the Wizards, John Wall had 21 points and eight assists but was ejected with 33 seconds left following a second technical foul.
Bradley Beal and Otto Porter bagged 20 points for the Wizards, who fell to 1-5 with the loss.