Bosh scored 23 points, including the winning 3-pointer with 1.9 seconds remaining, and the Heat beat San Antonio 88-86 on Sunday night with James, Wade and Mario Chalmers watching from the locker room as they sat out with injuries.
"We are the defending champs no matter who we put out there," Bosh said. "We are still the Miami Heat. We believe in ourselves. Each one of these guys is a professional. We played bigger roles in other cities but we came together and accepted lesser roles to win a championship here. We can still tap into that."
Ray Allen added 14 points, Norris Cole had 13 and Mike Miller 12 for Miami (58-15), which swept the season series with San Antonio (55-18). By earning the head-to-head tiebreaker with San Antonio, the Heat have a four-game cushion with nine remaining for the league's best record.
Miami beat San Antonio 105-100 on Nov. 29 when the Spurs opted to rest Tim Duncan, Tony Parker, Manu Ginobili and Danny Green.
All but Ginobili (strained right hamstring) played Sunday.
Duncan had 17 points and 12 rebounds and Kawhi Leonard added 17 points and 11 rebounds for the Spurs, who had a seven-game home winning streak snapped. Green and Parker added 12 points apiece and Stephen Jackson had 11.
Bosh finished 3 for 5 on 3s, including the final shot from straightaway in the closing seconds. He let out a loud yell after making the shot and celebrated with teammates when Parker's jumper bounced off the backboard as the buzzer sounded.
"He's a heck of a player, No. 1, but he's also a hell of a shooter," Spurs coach Gregg Popovich said. "He knocked down a big shot. Timmy contested it and he hit a big shot to win the game. Give him credit."
The game was similar to their first meeting this season, when the Spurs' reserves nearly toppled the Heat. This time the reserves prevailed, however.
"There's no question, it's a gratifying win," Miami coach Erik Spoelstra said. "To come in and play against a great team, an elite team. We talked about coming in with Miami Heat pride. It doesn't matter who's in uniform or not, all of our guys have proven that it's the pride of the name on the jersey, on the front of the jersey."
James and Wade were surprise late scratches while Chalmers did not play Friday in New Orleans and was listed as day-to-day with a sprained right ankle.
James strained his right hamstring in the first half of the 108-89 victory against the Hornets, according to the Heat. He continued to play despite the injury, however, scoring 36 points in 32 minutes prior to sitting out late in the blowout victory.
Wade injured his right ankle in Miami's 101-97 loss to the Chicago Bulls on Wednesday night, which snapped the Heat's 27-game winning streak. Wade had 17 points and nine assists in 33 minutes Friday against New Orleans.
The three did not join their teammates on the bench, choosing to stay in the locker room to watch the game. None were available for comment.
The absences didn't impact Miami.
"They played great tonight," Leonard said. "LeBron James, Dwyane Wade, Mario Chalmers didn't play, but the guys stepped up tonight and their coach had them prepared and ready to play."
Miami outscored San Antonio 31-18 in the third quarter, going 4 for 7 on 3s to take a 71-64 lead. Rashard Lewis' layup off a turnover gave the Heat a 64-56 lead, their largest of the game.
Leonard and Green hit back-to-back 3s as San Antonio pulled to 80-78 with 5:21 remaining in the game.
Duncan's jumper gave the Spurs an 84-83 lead with 2:59 to go. San Antonio had an opportunity to extend the lead when Green raced toward the basket off a steal, but Shane Battier blocked his 1-on-2 attempt. Parker pushed his hands down on the next stoppage of play, telling Green to take his time.
Both teams were scoreless until Duncan hit another fadeaway jumper with 1:21 left to give San Antonio an 86-83 lead. Cole hit two free throws to pull Miami to 86-85 with 32.1 seconds left, setting up Bosh's heroics.
Miami controlled the Spurs' pick-and-roll plays by double-teaming Parker with a bigger defender. Parker finished 4 for 14 with eight assists and one turnover.
"They just trapped me," Parker said. "They trapped me every time I did a pick-and-roll or any kind of play. They were trapping me the whole game."
The absences of James, Wade and Chalmers rekindled the controversy surrounding Popovich's decision to send Duncan, Parker, Ginobili and Green home instead of having them play the second game of a back-to-back Nov. 19 in Miami. It was the finale of a six-game road trip, finishing with four games in five days. The Spurs did not give the NBA or Miami prior notice of the players' absences, which led the NBA to fine San Antonio $250,000.
Spoelstra was asked if San Antonio's decision to sit their stars in Miami had an impact on his decision to rest his stars for this game.
"I could see how you guys can draw that conclusion, but no," Spoelstra said before the game.
Unlike Popovich, Spoelstra listed injuries as the reason for his stars' absence, which will likely eliminate the chance of the league fining Miami.
Popovich reacted in mock horror when told James, Wade and Chalmers were out.
"Are you kidding me," Popovich said in mock astonishment. "Who would think of something like that? That's below the belt. There's no place for that."
San Antonio led 45-40 at halftime.
NOTES: Two-time majors champion Rory McIlroy was in attendance, sitting alongside former Spurs forward and ESPN analyst Bruce Bowen. McIroy is in San Antonio to compete in the PGA Tour's Valero Texas Open, which opens Thursday at the AT&T Oaks Course. He won the 2012 PGA Championship and 2011 U.S. Open. ... Former Texas Rangers All-Star catcher Ivan Rodriguez received a loud ovation when he was introduced during the first half. Rodriguez was in San Antonio as part of the Big League Weekend, a pair of exhibition games between the Rangers and San Diego Padres at the Alamodome.Suggest a correction