Ridnour finished with 10 points and five assists for the Bucks, who have alternated wins and losses for the past nine games. Michael Redd had 24 points and Charlie Villanueva 23 in the win.
Vince Carter missed a triple-double by a rebound with 23 points, a season-high 14 assists and nine boards for the Nets, who saw their two-game win streak halted. Jarvis Hayes added 16 points in defeat and Bobby Simmons 15.
Yi Jianlian, who ended with 16 points, left late in the third quarter with a hand injury for the Nets, who made a season-high 16 three-pointers.
Up by three late in the fourth quarter, Redd hit an acrobatic jump shot to give Milwaukee some breathing room, 102-97, with 2:05 showing on the clock.
Two free throws from Carter made it 102-99 just prior to the one-minute mark.
The Bucks then had a chance to make it a two-possession game, but Charlie Bell missed a shot and Carter grabbed the rebound and called timeout with 17.1 ticks left to give the visitors an opportunity to get back into it.
The Nets inbounded the ball and Carter drove the lane but kicked it out to Simmons on the left wing for the game-tying three-pointer with nine seconds left.
Following a timeout, Ridnour took the inbounds pass, dribbled up top and then drove the lane and dropped in a teardrop floater.
The Nets failed to get a shot off on their final possession.
The clubs played to a 28-all tie after the first 12 minutes, but the Bucks opened a 61-49 lead at the break.
The Bucks' lead hovered around 11 points in the third until a Carter jumper and Brook Lopez layup brought it to 66-59.
The Nets kept pushing and cut it to 79-75 heading into the final frame.
A Bell jumper and three-pointer bookended a Ramon Sessions layup, which gave the Bucks an 86-75 lead with 10:15 left in the game.
Moments later, Carter's jumper and threes from Simmons and Keyon Dooling cut it to 95-90 with just over five minutes remaining.
Lopez' layup made it a three-point game with just under 2 1/2 minutes left.