World championship leader Kimi Antonelli was sixth fastest for Mercedes, one place behind McLaren’s Oscar Piastri.
The Italian’s title rival and team-mate George Russell was eighth quickest, 0.356secs behind Antonelli.
Antonelli leads the championship by 25 points as the season heads into what could be its halfway point, depending on whether the two Middle Eastern races due to finish the season can take place in the context of the war between the US/Israel and Iran.
Verstappen’s pace came despite Red Bull reverting to a standard rear wing while they refine the the ‘flip-flop’ or ‘somersault’ design that caused high-speed crashes for the Dutchman in the past two races.
The wing is the one with which Red Bull started the season, on which the flap opens for straight-line mode in the style of last year’s DRS overtaking aid, rather than rotating on its axis by more than 180 degrees.
The old wing is said to cost about 0.2secs of lap time around Spa-Francorchamps compared to the newer design, which may return for the next race in Hungary next weekend.
The session was relatively incident-free. The closest to an incident was Liam Lawson running a little wide after a big oversteer moment at Stavelot early in the session.
Piastri suffered a hydraulic pressure issue late in the session, forcing him to limp around the track with a minute remaining in the session.