Phoenix, with star guard Devin Booker sitting out because of a sore forearm, overcame a late seven-point deficit to force overtime on Kelly Oubre jnr’s three-pointer from the corner in the final seconds.
DeRozan, LaMarcus Aldridge and Dejounte Murray each added 18 for the Spurs (10-15).
Baynes, who only last week returned from a nine-game absence due to injury, came off the bench for the Suns and had 13 points and eight rebounds.
The Boomers centre/forward had a chance to win the game from beyond the arc but his buzzer-beater missed as the Suns lost their third of four and seventh of 10.
Ricky Rubio led Phoenix with 25 points and 13 assists as they drop to 11-14 on the season.
It was the second of the two games in the NBA Mexico City series this season, after the Dallas Mavericks beat the Detroit Pistons on Thursday.