The 22-year-old hit ten aces and won 77 per cent (53/69) of his first-serve points to advance in one hour and 53 minutes. He will now face Sebastian Korda, who edged out Kei Nishikori earlier on Thursday.
In a first set where both players dominated on serve, with Zverev winning 84 per cent of points (21/25) behind his first serve and Humbert 85 per cent (23/27), it was the Frenchman who claimed the opener in the tie-break when Zverev netted a forehand.
Zverev converted his first break point at the start of the second set when Humbert went long on the backhand to lead 2-0. From there, it continued with serve as Zverev dictated on the forehand to level. Humbert found the breakthrough in the fourth game of the final set though and was relentless from there, as he played aggressive tennis from inside the baseline to overcome Zverev.
Humbert defeated Sam Querrey in the first round and is now 11-13 this season. The Frenchman currently sits at No. 31 in the FedEx ATP Rankings having reached the semi-finals at the Open 13 Provence in Marseille (l. Herbert).
The third seed reached the semi-finals at Roland Garros last week (l. to Tsitsipas) and is now 24-10 on the season, having won the title at the Mutua Madrid Open (d. Berrettini) in May. Zverev, who reached the final in Halle in 2016 (l. to F.Mayer) and 2017 (l. to Federer), has yet to win a trophy on grass despite lifting 15 ATP Tour titles on clay and hard courts.
Earlier in the day, Lloyd Harris defeated Lukas Lacko 6-3, 7-6(8) in 87 minutes to advance to the quarter-finals. The 24-year-old, who is currently No. 51 in the FedEx ATP Rankings, hit 11 aces and saved the one break point he faced as he moved to 14-10 for the season. The South African’s reward is a meeting with either Nikoloz Basilashvili or Arthur Rinderknech.