Watson was pitched against a brilliant, awkward and resilient opponent, whose winning mentality ensured she prevailed over the young woman from Guernsey.
Williams expected raucous backing for her 23-year-old opponent, but at times she seemed genuinely taken aback by the level of support Watson was able to count upon. Williams later described it as the most fierce she has known at any Grand Slam.
But it was support Watson earned throughout a topsy-turvy match that eventually slipped away from her in three sets, 6-2, 4-6, 7-5.
At 33, Williams is still on course to secure the calendar grand slam. If she does achieve this aim, she will surely recognise this as being a pivotal stepping stone. Williams blinked back tears as she left the court, overwhelmed by the effort, and, perhaps, the potential significance of the victory. She refused to entertain further questions on her calendar slam ambitions afterwards.
Leaving aside there was clearly something not quite right with Williams, this was a towering performance from Watson, who grew into the game after a first set where there was little to suggest the drama to come.
She was given a rousing reception, including from the Aussie ‘fanatics’ who stayed on after failing to inspire Bernard Tomic to victory against Novak Djokovic. At times Watson conducted the singing, smiling the beatific smile noted by Williams earlier this week.
“She seems super-smiley,” she said. Watson almost – almost – became the smiling assassin last night. She wasn’t having it afterwards when someone wondered it she regarded this as the greatest day of her career. “No, I wouldn’t call losing the greatest day of my career,” replied Watson.
She struggled in the first set, overpowered by Williams in only 25 minutes. But Watson managed to fare better against her opponent’s serve in the next set, as unforced errors began to creep into Williams’ game. Remarkably, she had 33 compared to Watson’s 11 in the end. Such slackness gave Watson a way back into the contest, and she grabbed at this lifeline.
One of the key games was the sixth game of the second set, where Williams lost the first point on her own serve by sending an easy volley crashing into the net. Although she retrieved things by taking the game to deuce, Watson won the next two points, having to do little to secure the break thanks to Williams double-faulting, an error that was cheered to the rafters.
When Watson was herself broken straight away, many were left wondering whether it was a false dawn. But Watson shook off this disappointment to claim the next six games, remarkably. She even had a double-break in the third set, which she led 3-0.
Having not been broken at all in these championships, Williams was broken on five occasions in total, including to love in the ninth game of a gripping third set. It meant Watson served for the match.
Centre Court held its breath at first. But then, such was the cacophony as Watson fought back from 15-40 down, Williams requested an intervention from the umpire. Cue an outbreak of booing from the crowd. “I have never heard booing here before, that was a new one for me,” Williams said later.
Watson clawed back to deuce on two occasions as she fought to make it over the line before returning into the net to hand Williams a timely break. Deflation. Williams held her service game to love before converting her third match point to break again and see off her spirited opponent.
The winning point was a return-of-serve that landed plumb on the baseline.
Watson understandably called for Hawk-eye to be used, a last, desperate hope and a rather anti-climatic end to a riveting match.
Perhaps forgotten amid the excitement is that this victory sets up another must-see game in the fourth round, between Serena and her sister, Venus. Even this match-up will not come close to matching last night for drama. Watson had after all come so close to being the first British woman to defeat a reigning No 1 since Sue Barker defeated Chris Evert in Boston in 1979.
But Williams is not only a world No 1, she is five-times Wimbledon champion and holder of 20 grand slam titles. She is, perhaps, the great female tennis player of all-time. She displayed the traits of a true champion both in rallying to save this match, and then speaking with such warmth about Watson afterwards.
“She really gave her all,” she said. When questioned whether Watson’s ambition to break into the top 20 this year – she is currently at 56 – is a realistic one, Williams said: “Beyond the top 20; she can set her goals higher. She was playing so good, there was nothing I could do.”
“It’s not that I thought I was going to lose,” she added. “I just felt like she was playing really well. She just did everything so well. I wasn’t able to keep up. You know, sometimes you just don’t have your day. I thought maybe today just wasn’t my day. Obviously I keep fighting and I keep thinking, ‘Well, just let me keep trying to do the best that I can’.”
Hopefully Watson will experience more ultimately satisfying moments than this, but she will surely not have a better chance of overcoming Serena Williams.
Watson has complained of trolls making cowardly comments on her Twitter account. She lost here. But no-one, not even the cruellest bully, could criticise her efforts.