Sharapova's outings have been fleeting this week as she has dropped just five games en route to the last 16, spending a total of two hours and 54 minutes on court over her three matches.
On Saturday, it took her 66 minutes to subdue her 28th-seeded opponent on a sunbathed Court Phlippe Chatrier with another display of power and accuracy.
Sharapova, twice a semi-finalist on Parisian clay, will next face the unseeded Czech Klara Zakopalova.
Chinese seventh seed Li, who last year became the first player from an Asian nation to win a singles Grand-Slam title, needed almost two hours on a sunsoaked Court Suzanne Lenglen to break the world number 36's resilience.
Li struggled with her serve and fell a break down in sixth game but immediately broke back. But McHale had more pace and broke again to bag the opening set after 48 minutes.
Li upped her game in the second, finding better angles to open a 4-1 lead and steal her the opponent's serve again to level the tie.
She reeled off five games in a row in the decider to wrap it up and set up a last-16 meeting with Kazakh qualifier Yaroslava Schvedova.
Fourth seed Petra Kvitova moved into the French Open fourth round with a 6-2 4-6 6-1 victory over Russian Nina Bratchikova, but the Czech was forced to toil in the piercing Parisian sunshine.
Peppering the baseline with a series of snappy and accurate groundstrokes, Kvitova had looked to be on course for a smooth passage into the next round when she claimed the first set in just 28 minutes.
The Russian, however, upped her intensity in the second, forcing the match to a decider before Kvitova regained the upper hand to close it out with a double break.
She will now play Varvara Lepchenko, who knocked out 2010 champion Francesca Schiavone.
Schiavone was beaten for the second time in a month by the American left-hander.
Lepchenko, ranked 63rd in the world, beat the 2010 winner and 2011 runner-up 3-6 6-3 8-6 in a match full of long rallies in the midday sun on Court One, where the temperature reached 29 degrees Celsius.
Italian Schiavone, the 14th seed, lost in the first round to the Uzbekistan-born Lepchenko on Madrid's blue clay last month, and said before Saturday's game that she found playing left-handers troublesome.
After three exchanges of break in the third set, Lepchenko broke again to go 7-6 up and then saved four break points before smashing a winner on match point.
Also perishing on day seven was a livid Caroline Wozniacki.
Former world number one Wozniacki's slide continued when she was dumped out of the French Open third round by Estonia's Kaia Kanepi, losing her temper in the process.
The Dane, seeded ninth, slumped to a 6-1 6-7 6-3 defeat after a controversial line call went against her at 1-1 in the deciding set after she had battled back into the match.
Wozniacki, who finished each of the last two seasons on top of the rankings despite not having captured a Grand Slam title, had a heated debate with chair umpire Poncho Ayala.
"When the ball is clearly out I don't think there should be anything to argue about," she said. "If they cannot see, they should have other umpires on the lines or invent Hawk-Eye on these courts.
"It's a disgrace mistakes like this are made. It wasn't even like it could have been in, could have been out. It was clearly out," said Wozniacki.
"When a ball travels five miles an hour in the third set at 1-1 I think either the linesman or the main umpire should be able to see the ball."
Wozniacki won six titles in each of the 2010 and 2011 seasons but has yet to get off the mark this year.
She recently began working with new coach Thomas Johansson to halt the decline and still believes she can salvage the year.
"I can't really be happy about losing today but it's sport and, at least looking ahead, you have big tournaments coming up, Wimbledon and the Olympics, US Open, so there is still plenty to look forward to," the 21-year-old said.
"I just have to stay positive and in tennis there is always next week. So that's the good thing."