Playing his first event since his heartbreaking defeat to Novak Djokovic in the fourth round at Wimbledon, the Australian No.1 claimed a morale-boosting 7-6 (7-5) 6-2 win to set up a last-16 clash with Czech Jiri Lehecka.
As seventh seed at the tournament, de Minaur was favourite to see off world No.75 Bu. Now the Australian can take heart from a solid performance at the hardcourt ATP 500 tournament as he builds towards next month's US Open, where last year he reached his third consecutive grand slam quarter-final.
De Minaur has enjoyed previous success in the American capital. In 2018, then ranked No.72, he made a surprise run to his first ATP 500 final, where he lost 6-2 6-4 to Germany's Alexander Zverev.
Now 26, the world No.13 will look to make further progress at the Washington Open after racking up his 280th career win and 31st this season as he continues his quest to return to the top 10.
However, there was no such joy for De Minaur's compatriot Aleksandar Vukic, the Sydneysider suffering a 6-3 6-2 defeat to top-seeded Taylor Fritz.
The American was making his first appearance since his impressive semi-final run at Wimbledon, where he gave Carlos Alcaraz a real test.
Fritz got his North American hard-court season off to a strong start by hitting 11 aces and saving the only break point he faced.
He will be trying to replicate last year's strong showing in this portion of the season, when he reached his first grand slam final at the US Open.
After getting a first-round bye, Fritz next plays in the third round against Italy's Matteo Arnaldi, who eliminated No.16 seed Lorenzo Sonego 7-5 7-5.
There was no joy for Australia's world No.24 Alexei Popyrin, who bowed out after a bruising 7-5 5-7 6-3 defeat to China's Yibing Wu, who claimed his first win over a top-25 player in over two years in two hours and 37 minutes.
Other seeded men advancing included No.8 Daniil Medvedev, of Russia, who beat American Reilly Opelka 3-6 7-5 6-1, and No.9 Flavio Cobolli, of Italy, who beat Japan's Yoshihito Nishioka 6-2 7-6 (7-3).
However, fifth-seeded Russian Andrey Rublev was a 7-5 6-2 loser against 19-year-old American Learner Tien, who has now logged four wins over opponents ranked in the top 10 this season.
- with Agencies
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