The Spaniard is bidding for his first ATP indoor title this week.
Defending champion Elena Rybakina fought off Ons Jabeur in three sets and American Ashlyn Krueger reached her first WTA 500-level semifinal.
The World No.4 was dominant in every phase of the game in Dallas on Wednesday night.
Daniil Medvedev saved a match point in the second set, but fell in three to Italian qualifier Mattia Bellucci.
Defending champion Elena Rybakina beat qualifier Katie Volynets 2-6, 6-4, 6-4 to score her fifth straight win at the Mubadala Abu Dhabi Open.
Defending champion Tommy Paul held off Jenson Brooksby 6-7(6), 6-3, 6-4 for his fifth straighht Dallas Open victory.
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