The Wizards also snapped New York's 10-game winning streak over them.
Wall, playing in front of his college coach, John Calipari, and Hall of Famer Magic Johnson, scored 10 points in the fourth quarter as Washington took control.
Ariza, who missed 17 games with a left calf injury earlier this season, has played solidly and more often in recent games, and his four-point play to start the fourth quarter gave the Wizards a 74-73 lead. His 3-pointer pushed Washington's advantage to 88-80 with 8:36 to play.
New York never got closer than 97-92 with 2:57 to play and the Wizards pulled away at the end.
Martel Webster added 19 for Washington, which has won just 13 games, but has beaten five of the six NBA division leaders.
Carmelo Anthony led the Knicks with 31 points. Amare Stoudemire scored 19 and Raymond Felton had 17.
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It was a highly entertaining first quarter with both teams shooting over 50 percent and only five combined fouls. Washington raced to a 16-5 lead in the first 4 1/2 minutes, but New York led 29-28 after one.
The second quarter was a much slower-paced one, with neither team taking more than a four-point lead and the Wizards scoring the last six points of the half to lead 51-48 at the break.
In the third, Washington took a seven-point lead early in the quarter, but the Knicks scored nine straight points near the end and led 73-70 going to the fourth.
NOTES: New York coach Mike Woodson told reporters at Wednesday's shootaround that F Rasheed Wallace, who hasn't played since Dec. 13 with a sore left foot, should return to practice after the All-Star break. ... Washington G Bradley Beal missed his fifth straight game with a sprained right wrist. ... Wall and Stoudemire were assessed technical fouls for pushing each other late in the first half. ... New York C Tyson Chandler had 13 rebounds. He had 20 in each of his previous three games, tying a team record.
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