Three-times champion Rafael Nadal cruised past John Millman and Nick Kyrgios swept past Steve Johnson as both seeds avoided US Open shocks.
Millman delivered the upset of the tournament last year when he beat five-times winner Roger Federer in a surprising run to the quarter-finals but he was unable to recreate the same magic against the relentless Spanish second seed, who won 6-3 6-2 6-2.
Nadal, who last year retired from his semi-final with a knee injury after several gruelling matches, was a model of efficiency in his opening match of the year's final Grand Slam.
The 33-year-old Spaniard seemed to get better as the match went on and made quick work of Millman in the final set where he went up an early double-break for a 3-0 lead.
Nadal faced only three break points and easily turned aside each one. The first was in the opening game of the match, with Millman's other two chances to break coming in the final game of the second set.
Kyrgios had a similarly easy path into round two, beating Johnson 6-3, 7-6 (1), 6-4.
It was nearly midnight when the last match of the day started but Kyrgios kept the crowd awake with his usual mixture of great tennis and bad language, including a warning in the second set for cursing after he was angered when a fan moved behind the baseline.
But minutes later he summoned some of his best tennis to prevent Johnson from getting into the match, seizing a 6-0 lead in the tiebreaker. He capped that run by sprinting to chase down a drop shot, then strutting near the net after winning the point.