Booker had a hot hand sinking 15 of 19 field goal attempts for 40 points.
Simmons was also outstanding, leading the 76ers with six points, five rebounds, six assists and equalling his career-high seven steals.
The 76ers entered the game as the only undefeated team in the league after opening the season with five wins.
The Suns, atrocious the past four seasons, also started the season on a high with the off-season additions of veterans Baynes, Ricky Rubio and Dario Saric.
The win gives the Suns a five-win, two-loss record.
Baynes, traded from the Boston Celtics to the Suns in the off-season, was surrounded by plenty of familiar faces.
Philadelphia coach Brett Brown coached Baynes and the Boomers at the 2012 London Olympics and was instrumental in the San Antonio Spurs signing the big Queenslander months later.
Baynes was also facing his former Celtics teammate Al Horford, who joined the 76ers in the off-season.
The 76ers’ other Australian, Jonah Bolden did not play.
In other NBA games on Monday, Kyrie Irving had 39 points to lead the Brooklyn Nets to a 135-125 win over the New Orleans Pelicans.
The Washington Wizards beat Thon Maker’s Detroit Pistons 115-99 and James Harden dropped 44 points in the Houston Rockets’ 107-100 victory over the Memphis Grizzlies.