But on the next possession, Ridnour got a screen and Simmons slipped to the floor rotating on defense, giving the point guard the lane for the easy floater that rolled around the rim before falling in for the victory.
Michael Redd, held scoreless over a 31-minute span, hit a 3 to give Milwaukee a 100-93 lead with 3:11 left. Vince Carter, who finished with 23 points, 14 assists and one rebound short of his fifth triple-double, hit a fadeaway jumper and set up a layup by Brook Lopez to make it 100-97.
Redd added a jumper and Carter answered with two free throws to make it 102-99 as the Nets cut a 14-point lead down by hitting 16 of 30 3-pointers, one off the franchise mark of 17.
After both teams failed to score on their next possession with less than a minute to go, the Nets had one chance left with 17 seconds remaining.
Carter drove the lane, kicking to Simmons for the 3 that looked to send the game to overtime until Ridnour's winner.
Jefferson struggled in his first game against the team he spent seven years with, finishing 3-of-15 from the field for 13 points.
Milwaukee got 23 points from Charlie Villanueva, 11 from Ramon Sessions and 10 each from Ridnour, Luc Richard Mbah a Moute and Charlie Bell.
Yi scored 16 points, but left late in the third quarter after injuring his right hand. Jarvis Hayes also scored 16 for the Nets, and Simmons and Dooling had 15 apiece.
The Nets traded Jason Kidd, the cornerstone of a team that reached the playoffs six straight times and the NBA finals in 2002 and 2003, last season for Devin Harris, who missed his second straight game with a balky right hamstring.
Jefferson was the next to go, but he and Carter remain close.
The two had a playful chat near the Nets bench just before the start of the second half that left Carter giggling as he walked away to join his teammates in the huddle.
Notes: Milwaukee snapped a four-game losing streak to New Jersey. The Nets have still won nine of the last 11 in the series. ... Milwaukee fans booed Yi each time he touched the ball after feeling that he didn't give the city a chance when his adviser gave indications he wanted to be traded after last year's draft and took several weeks to sign a rookie contract. ... Simmons was the NBA's Most Improved Player with the Los Angeles Clippers in 2004-05, which led to his $47 million, five-year contract with Milwaukee.