The 65-minute first set couldn't have been closer - Li even had four set points serving 5-4, missing two of them off forehand errors and the other two off Radwanska backhand winners. And once those four set points evaporated it was Radwanska who capitalized, sneaking out the first set in a breaker.
Radwanska looked headed for a straight set win as she built a 4-2 lead in the second set, but Li was not done by any means - she reeled off the next four games, the last few games of those littered with winners from both wings, and snuck out the set, sending their quarterfinal match into a decider.
After a slight delay of play to close the Centre Court roof Radwanska came out sharp and refreshed, breaking in the opening game of the third and racing out to a 5-1 lead - that's when the drama began.
Serving at 1-5, Li fought off two match points - one off a forehand swing volley winner, one off a forehand drop volley Radwanska couldn't put back in the court. Li held and closed the gap to 2-5.
Then came the epic game. Serving at 5-2, Radwanska missed her third match point with a double fault and watched on as Li fought off another four match points, one with a volley winner, another with a clean forehand winner, then two more with big backhand returns that Radwanska couldn't, well, return.
It was eighth time lucky for the No.4-seeded Radwanska though, as she drew one last error from the No.6-seeded Li to close out the two-hour, 43-minute marathon, which was of the highest quality, too - Radwanska had a +14 winners-to-unforced errors differential (32 to 18) and Li had +18 (58 to 40).
"We've played so many times before, but that match was really, really good, on a really high level," Radwanska said afterwards. "From the first point to the last point it was a really great battle. She was playing very well today. And I'm even double happy I could beat her playing very good tennis.
"I think this was the match where we proved Top 10 players are playing really good matches."
On one of Li's set points in the first set, she hit a first serve that was called out, but on replay it was shown to have hit the line, which would have made it an ace - Li was told about it afterwards.
"It was in? Why are you telling me now!" she joked. "Wow. Next time I will challenge it for sure."
Radwanska pulled off a number of her trademark 'squat shots' during the match, but after going to three sets in her last two rounds as well, she was understandably exhausted after the encounter.
"My last two matches were similar, I think 2:40 on court - it's a lot, especially on grass, where everything comes from your legs," Radwanska said. "I was really struggling today as well, but this is the quarterfinals of a Grand Slam and I was really pushing myself, even 200%, to fight to the end."
How much pain would she be able to take? "I don't really know how much - I think there's no limit."
For years Radwanska had a quarterfinal block at the Grand Slams, but last year at Wimbledon she broke through - now, at the same Grand Slam, she breaks it again. Does she feel any pressure?
"I think the bigger pressure was in the first week," Radwanska said. "I think the quarterfinals is the minimum for everyone, especially when you're seeded. But when I got to the quarterfinals I think I've been more relaxed. And the semifinals are already a great result. I'm not feeling any pressure.
"Of course I made the final last year, but that actually helps, as this isn't the first time now."
Li may not have made the semifinal cut, but she certainly proved her spring slump is over - since her blistering first four months of the year, she suffered a string of early losses in May and June.
"It was a pretty good tournament really - at least better than I did here the last two years," Li said. "And also I proved another thing - before I never thought I could come to the net as many times as I did today, so now Carlos and I have a job to do - we know what to do to make the next step."