Five-time champion Venus Williams rallied from a set down to beat Japan's Kimiko Date-Krumm in a match of breathtaking drama under the roof on Wimbledon's Centre Court.
Date-Krumm took an incredible first set on a tie-break but only after Williams had battled from 5-1 down and saved a total of seven set points.
At times, the tennis was of the highest quality as Date-Krumm attacked Williams' serve and the American scrapped her way back into the set.
Eventually, the 40-year-old Date-Krumm - a Wimbledon semi-finalist in 1996 - clinched the first set in one hour and four minutes but by then Williams had found her rhythm.
The American moved a break up early in the second set to draw level in the match before prevailing in a hard-fought third to clinch a 6-7 (6/8) 6-3 8-6 victory in nearly three hours.
Williams will face either Monica Niculescu or Maria Jose Martinez Sanchez in the third round.
The roof was closed over Centre Court as the rain fell over the rest of Wimbledon - but Williams and Date-Krumm offered the watching Duchess of Cornwall some high-class entertainment.
Date-Krumm broke in Williams' first three service games as she raced into a 3-0 lead in just nine minutes, and then opened a 5-1 advantage.
Williams' year has been badly disrupted by a hip injury she suffered at the Australian Open and she only returned to action at Eastbourne last week.
Date-Krumm was too hot for Williams to handle in the opening exchanges and she raced into a 3-0 lead in just nine minutes with some pinpoint baseline winners.
Williams secured one break back but immediately lost it again as Date-Krumm added some dream volleying to the winners she had been peppering past the American.
But Williams refused to buckle. Her grunting got louder and she saved three set points to string together five consecutive games to heap the pressure back on Date-Krumm.
Date-Krumm twice failed to serve out the match but she was happy to attack Williams' powerful serve and opened a 6-2 lead in the tie-break to earn four more set points.
Williams hit back again, saving all of them to draw level before Date-Krumm finally edged a set ahead.
It was an impressive show of mental fortitude from Kimiko-Date, who spent 12 years in retirement before returning to the circuit in 2008.
On the way to holding serve in the first game of the second set, Date-Krumm switched her racquet from right hand to left to play a lob after she had been forced out wide.
She is naturally left-handed but learned to play with her right to fit in with Japanese custom.
But Williams levelled with a blistering winner and then sealed the first break of the second set after Date-Krumm, who had volleyed with such dexterity, planted one into the net.
Date-Krumm earned two break back points but Williams' serve had cranked up a gear and she saw them off to wrap up the set before quickly moving a break up in the decider on the back of her powerful forehand.
Williams gifted Date-Krumm a break back with only her second double fault of the match after being deceived by a flick of the net cord earlier in the game.
Date-Krumm had to save three break points to hold in a 10-minute game, one of them on a challenge which showed the ball had just brushed the line.
Each game was fiercely contested but, with Williams' power and some great volleying from Date-Krumm, the set went with serve until it was 7-6.
And it was Date-Krumm who blinked first.
Serving to stay in the match for the third time, she conceded two match points and Williams wrapped up a memorable victory when Date-Krumm's backhand crept wide.