So facing a break point early in the second set, Williams conjured up a backhand passing shot so good, so powerful, so precise that Sharapova had no chance to reach it. Williams watched the ball land in, then raised a clenched left fist toward the night sky.
In her first match at the US Open since last year's loss in a chaotic, controversial final, Williams stretched her winning streak against Sharapova to 19 matches with a nearly flawless performance that produced a 6-1, 6-1 victory devoid of drama Monday night.
"Every time I come up against her,'' Williams said, "I just bring out some of my best tennis.''
She sure did this time; the whole thing lasted all of 59 minutes.
Williams won twice as many points, 56-28. She saved all five break points she faced and lashed serves at up to 115 mph. She broke five times.
"I always said her ball somehow lands in my strike zone,'' Williams said. "I don't know. It's just perfect for me.''
Few players would have stood a chance against Williams the way she was hitting balls deep and true -- and certainly not a diminished Sharapova, who is ranked just 87th after missing much of this season with a bad right shoulder that needed surgery.
"Bottom line is I believe in my ability," Sharapova said after the match. "You can write me off. There are many people that can write me off, especially after going down 6-1, 6-1. As long as it's not the person that's inside of you, you'll be OK."
Williams arrived at Flushing Meadows, where she has won six titles, accompanied by questions about her back because spasms that flared up earlier this month forced her to stop playing during the final of one hard-court tune-up tournament and withdraw from another.
That didn't seem to be an issue against Sharapova.
"The body's good. I feel good,'' Williams said. "My back's a lot better. So I'm excited. This is going to be fun.''
A year ago, she was beaten by Naomi Osaka in straight sets in a US Open title match that devolved after a back-and-forth between Williams and chair umpire Carlos Ramos. When Williams was asked Monday night what she thought of the U.S. Tennis Association's decision that Ramos would not officiate any match involving her or her older sister, Venus, at this year's tournament, this was the reply: "I don't know who that is.''
Williams was as calm and cool as can be against Sharapova, only rarely showing emotion with a cry of "Come on!'' or the occasional fist pump, such as the one after the key backhand on break point.
Sharapova called that shot "great.''
It shaped up as far and away the most intriguing matchup on Day 1 at the year's last Grand Slam tournament.
Few athletes in any sport have been as popular in recent decades. Williams owns 23 major singles title and Sharapova five. Both have a career Grand Slam. Both have been ranked No. 1.
Although there were several other matches involving big-time players on Monday, nothing brought out the spectators the way Serena Williams vs. Maria Sharapova did, with full-throated roars greeting them when they walked from the locker room into a dimly lit stadium.
When the lights came on, Williams proved far more ready for prime time.
Only once before had Sharapova lost a night match in Arthur Ashe Stadium.
"I've had a lot of tough matches here and a lot of tough losses,'' she told the crowd afterward, "but coming out here tonight makes it all worthwhile.''
The Associated Press contributed to this report.