The 18-year-old Auger-Aliassime hit 30 aces and will next play compatriot Milos Raonic, last year's finalist. The sixth-seeded Raonic defeated Hungary's Marton Fucsovics 6-4, 6-4 at the grass-court tournament.
Auger-Aliassime, who is bidding to reach his third tour-level final, saved Brown's only match point at 5-4 in the third set and won in just under 2½ hours. It was the first time he played three tiebreakers in a single match as a professional.
Brown, who started the week looking for his first tour-level match win since the 2017 US Open, upset the top seeded Alexander Zverev on Thursday. Italy's Matteo Berrettini will play Jan-Lennard Struff in the other semifinal. Berrettini defeated Denis Kudla of the United States 6-3, 6-3, while the German player progressed with a 6-4, 6-4 win over Lucas Pouille.
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