The Russian defeated Schnyder - who, at 39, is the oldest player ever to make the main draw of a Grand Slam via qualifying - 6-2 7-6 (8-6).

The match was Schnyder's first in a Grand Slam since she came back to tennis in 2015 having retired in 2011.

"I knew I was in for a battle no matter her story or my story," said Sharapova.

"For her to come back and have the desire is really admirable. I'm just really happy I was able to win that last point."

Sharapova, 31, will play Romanian Sorana Cirstea in the second round in New York.

Schnyder, who reached the quarter-finals at Flushing Meadows in 1998 and 2008, said: "It actually doesn't feel so special and it doesn't feel like I've been gone for such a while. It has been part of my life for so long."

In their first meeting in 10 years, world number 186 Schnyder was handed an early break by Sharapova - who was crowned US Open champion in 2006 - after the Russian made three double service faults in the opening game.

Serving did not improve on either side of the net with the first four games all breaks, before Sharapova held for the first time to take a 3-2 lead.

From there, the 22nd seed dictated the first set, taking it in 40 minutes, and looked to have eased through the second having built a 5-1 advantage.

But errors started to creep into Sharapova's game allowing Schnyder to level at 5-5 before forcing the tie-break, in which Sharapova - who hit 23 winners but made 46 unforced errors - needed four match points to seal victory.