Van Aert will have to wait until the stage 13 race against the clock at the Tour to try out this new garment, which he won by covering the 38.2km course in 44:47, 32 seconds better than Deceuninck-QuickStep's Yves Lampaert and 39 seconds better than Lampaert's teammate Remco Evenepoel. Defending champion Victor Campenaerts (Lotto Soudal) finished fourth, 1:05 down.
Thursday's win was Van Aert's third of the season so far after he won the individual time trial at Criterium du Dauphiné, followed by a sprint stage the next day. The 24-year-old is going into his first Tour with a full head of steam along with his new jersey.
"[Jumbo-Visma] performance manager] Mathieu Heijboer coached me very well," Van Aert said of managing Thursday's effort. "He said I was in the lead, but it was a game of seconds and I had to keep going. He did not reassure me and I had to fight until the finish."
Van Aert said he started to get excited about the possibility of winning a Belgian jersey a couple fo weeks prior to the race.
"This jersey has a lot of value now, because there was a strong field of participants," he said. "I am very happy that I was able to win today. I now have everything I need to perform at top level: good legs, top material and top guidance."
Heijboer said Jumbo-Visma started training in the time trial with Van Aert right after the Classics.
"We knew that he has a lot of potential as a time trial rider," Heijboer said. "He has been tested extensively to fine-tune his position on the bike, which resulted in a faster time trial. In addition, Wout has trained a lot on the time trial bike. When he won the time trial in the Dauphiné, we knew that he had a good chance to win today. This was his main goal for the month of June and it is great that he succeeded."
Jumbo-Visma have not yet released their official Tour de France roster, but it is expected that Van Aert will be joined there by sprinter Dylan Groenewegen, GC rider Steven Kruijswijk, German time trial specialist Tony Martin, Kiwi climber George Bennett, Norway's Amund Grøndahl Jansen, Belgian Laurens de Plus and Dutchman Mike Teunissen.
The Tour de France begins Saturday, July 6, in Brussels and concludes Sunday, July 28, on the Champs-Élysées in Paris.