The reserve swingman had a career-high 18 points, Kawhi Leonard scored 10 of his 24 in the decisive third quarter and the Spurs beat the Milwaukee Bucks 123-98 on Monday night for their fifth straight victory.
San Antonio set a season high for points, two days after posting 121 against Houston, and Simmons made a big impression on Joe Prunty, the Bucks' interim coach.
"One of the biggest differences was Jonathan Simmons," Prunty said. "He really came in and affected the game. His energy, his effort, pushing the ball down the floor and how aggressive he was. He really impacted the game."
Simmons went 6 for 7 from the floor, made six of seven free throws and committed only one turnover. He made his debut Nov. 14 after spending last season with the Austin Spurs, San Antonio's NBA D-League affiliate.
"The aggressiveness is the first thing that stands out," Prunty said. "His mindset was to attack. He played really hard on both ends of the floor. The aggressiveness of Jonathan Simmons was very contagious. That said, it was a very good team game for them. I just thought he was the catalyst."
LaMarcus Aldridge had 16 points and 11 rebounds, and Tim Duncan finished with 14 points and 10 boards for the Spurs, one game after going scoreless for the first time in his 19-year career. He received a nice round of applause from the crowd when he went to the bench with 5:43 left.
The Spurs improved to 30-6 and joined defending champion Golden State as the only teams to reach 30 wins already this season.
"(It's) the same thing. They move the ball. They play good defense," said Milwaukee's Greg Monroe, who had 15 points and eight rebounds. "They have a championship pedigree. They know what it takes to win. Every night they play hard, they play together. They trust each other."
San Antonio was without starting point guard Tony Parker due to right hip soreness, but still won its 27th game in the last 31.
Patty Mills, filling in for Parker, and Leonard engineered a 9-2 run that gave the Spurs an 18-point lead late in the third quarter. Mills hit a 3-pointer, Leonard converted a three-point play and Mills sank his third 3 of the period as San Antonio pulled away.
Simmons and Aldridge sparked the Spurs' momentum-shifting second quarter. Simmons scored 12 points on 4-of-5 shooting from the floor and Aldridge added six points as San Antonio outscored Milwaukee 31-19 to lead 60-49 at halftime.
"(Leonard) has been great at both ends of the floor," Spurs coach Gregg Popovich said. "He is one of very few two-way players in the league at that level."
Khris Middleton scored 19 points to lead the Bucks, who put all five starters in double figures. But the combined effort wasn't nearly enough as Milwaukee lost its eighth straight to the Spurs.
The Bucks entered first in the NBA in points scored in the paint, but the Spurs outmuscled them inside by a 60-42 margin.
"We knew that was a strength of theirs," Popovich said. "So we tried to take it away as best we could."
Jerryd Bayless sustained an apparent injury to his left ankle after getting tangled up with Mills on a drive to the Bucks' basket in the second quarter. Bayless fell to the floor and remained there for a few moments. He got up and walked off the court.
Popovich picked Johnnie O'Bryant to shoot the two free throws.
No immediate medical update was available on Bayless, but he had crutches next to his locker. He sprained the same ankle in Detroit on Dec. 4 and missed 11 games.
Spurs: Duncan bounced back nicely after failing to score in 14 minutes of Saturday's victory over the Rockets. ... The bench outscored the Bucks' reserves 56-23. ... Simmons' previous career high was 14 points on Dec. 7 at Philadelphia. ... Mills made his first start of the season filling in for Parker at point guard. Parker did not travel with the team. ... Danny Green hit a 3-pointer in the first half and needs two more to pass Bruce Bowen (661) for second place on the Spurs' career list.
Bucks: The NBA fined guard O.J. Mayo $25,000 for aggressively pursuing a game official and failing to leave the court in a timely manner following his ejection Saturday. Mayo had to be restrained after being assessed a second technical foul early in the first quarter of Milwaukee's 95-85 win at Minnesota. "You play with emotion, passion, but we have to make sure we keep our composure and handle things the way they should be handled," Prunty said. "It's definitely something that you teach from and speak to all the guys about."
San Antonio has swept the season series against Milwaukee for four consecutive seasons.
Spurs: Host Utah on Tuesday night.
Bucks: At Chicago on Tuesday night.
Stephen A. Smith says Westbrook is the most "ruthless and vicious" player on the court. Has Westbrook actually humbled the unanimous MVP?
Tim Legler says Cleveland needs to change its approach in Game 5 having LeBron James and Kyrie Irving getting inside and getting to the free-throw line and being less of a finesse and perimeter oriented team.
Kara Lawson breaks down how Oklahoma City's defense is forcing Stephen Curry into making poor decisions.