(CNN)Haven't we seen this from Serena Williams before?
Yes, in fact, only a few weeks ago.
It was at the French Open when the world No. 1 toiled, needing to rally from a set down four times and coming back from a break deficit in the third set of the final against Lucie Safarova. She ultimately landed a landmark 20th major.
On Friday at Wimbledon in London, Williams dug deep to fend off home favorite Heather Watson 6-2 4-6 7-5 in the third round, keeping alive her hopes of completing the "Serena Slam" for a second time and winning all four majors in a season.
But the 59th-ranked Watson -- roared on by the British faithful on Center Court -- gave Williams her toughest match this summer. She was two points away from victory in the third set, when the American appeared to cry.
"I honestly didn't think I ... was going to win," Williams told reporters. "How I pulled through, I really don't know. I just was like, listen, if I'm going to go lose, I'm going to lose trying to do the right things."
She subsequently said she wasn't about to answer any more questions about the "Serena Slam" -- winning four straight majors -- or the possibility of claiming all four majors in one season. Perhaps the pressure played a part in Friday's outing, then.
Not since 1979, when Sue Barker -- who has long fronted coverage for Wimbledon's host broadcaster, the BBC -- downed Chris Evert had a British woman upset a world No. 1 but oh, how Watson indeed came close.
Williams must have flashed back to Wimbledon one year ago, when she was ousted in the same round by a similar type of counter-puncher, Alize Cornet.
In presumably a relief for Williams, she has two days to recover -- mentally and physically -- before meeting older sister Venus Williams in the fourth round.
It's their first matchup at a grand slam in six years and Serena claimed after Friday's performance that her sibling has the edge.
"Well, I think no matter how Serena's playing, she knows how to win," said Venus Williams. "I think I'm playing very well actually. Just have to keep that up."
Venus Williams, like Serena a five-time Wimbledon champ, had no such troubles Friday, routing Aleksandra Krunic 6-3 6-2.
In an absorbing third set on Center Court, Watson led by two breaks at 3-0. With Watson keeping balls in play and making Serena Williams hit extra shots, the latter duly produced unforced errors.
There were 33 overall, a telling figure on grass -- rallies generally tend to be shorter, lessening the error count.
Watson -- who saved three match points in the first round against Caroline Garcia -- even had a point for 4-0, though Serena Williams broke for 3-1.
"I remember in that game I just kept saying to myself, 'This is really important, this game,'" said Watson. "It would have just gotten me that bit further ahead, that bit closer."
And when Watson relinquished serve from 40-0 to make the score 3-3, many probably thought her chance was gone -- especially as she then trailed 4-3.
But Watson claimed the ensuing two games for an opportunity to serve it out at 5-4.
Watson is in the midst of revamping her game after suffering from glandular fever, wanting to be more aggressive. It showed when she saved a third break point with an ace.
Serena Williams, however, is difficult to put away and got her reward through an unforced error to level.
Serving at 5-6, Watson managed to fend off two match points on the ad side as Serena Williams struck almost two identical returns into the net.
Third time was a charm for Serena Williams when she powered a backhand cross-court that forced a Watson backhand error. Serena Williams thought her ball was long but to her delight, Watson's challenge showed the ball to be in.
Serena Williams trudged to the net, worn down by the day's proceedings and just thankful to prevail.
She'll now fully turn her thoughts to Monday. Serena Williams holds a 14-11 lead against Venus and is 3-2 at Wimbledon, where their previous duels had all been in semis or finals.
Venus, though, won their last head-to-head overall, in Montreal a year ago.
"It's unfortunate that it's so soon," said Serena Williams. "But we're going to do the best that we can. I mean, she's my sister today. She's my sister next week. She's my sister next year.
"I think that's a little more important than a match. We'll leave everything out on the court. When it's done, we'll go back to regular life."