Rio de Janeiro - Defending champion Serena Williams ended a three-match losing streak against France's Alize Cornet to keep her hopes of a fifth Olympic gold medal alive on Monday.
But it was a rollercoaster 7-6 (7/5), 6-2 victory for the 34-year-old world No 1, who 24 hours earlier had suffered her first ever Olympic Games women's doubles loss with sister Venus.
Cornet had defeated the American star three times in 2014, including at Wimbledon, and she proved to be a thorn in her opponent's side again in Rio.
Williams led 3-0 and had two points for a 4-0 advantage in the first set.
But Cornet stormed back, forcing the American to save two set points in the 10th game before the top seed sealed the tiebreak after 77 minutes on a chilly centre court.
Williams stepped on the gas in the second set to secure a third round clash with Ukraine's Elina Svitolina, securing victory on a third match point.
Juan Martin del Potro followed up his shock defeat of Novak Djokovic by downing Portugal's Joao Sousa in front of a legion of passionate, vocal Argentine fans.
The giant 27-year-old, ranked at 141 in the world after years of wrist injury misery pushed him to the brink of quitting, swept to a 6-3, 1-6, 6-3 win.
He goes on to face Japan's Taro Daniel where he will start favourite, especially if he again musters the support of the fans who turned centre court into a little corner of Buenos Aires on Monday.
Dressed in sky blue football shirts, they draped national flags and banners over the barriers and responded defiantly when locals booed the mention of del Potro's name.
However, traditional bitterness between Brazil and Argentina boiled over when a group of fans engaged in a punch-up.
"I hope that will not happen again because people need to enjoy the matches and we need to have peace between Argentina and Brazil. This is not football," said Del Potro.
The 2009 US Open champion said he was running on empty by the end after only getting to bed at 4:30 in the morning.
"It was really hard for me. I cannot believe my match from last night and I already won another match at the Olympics.
"I only had five hours' sleep but I'm very glad with my success. I played really well at the end of the match and I think that was the key."
Things got even better for Del Potro moments later when French fifth seed Jo-Wilfried Tsonga, a potential quarter-final opponent, lost 6-4, 6-3 to Gilles Muller of Luxemburg.
German second seed and Australian Open champion Angelique Kerber recovered from a 4-1 first set deficit to defeat Canada's Eugenie Bouchard, 6-4, 6-2.
It was Kerber's first win over the 2014 Wimbledon runner-up in three years.
Kerber next faces Australia's Samantha Stosur who was too strong for Misaki Doi of Japan, winning 6-3, 6-4.
Spain's Garbine Muguruza, the French Open champion, routed Japan's Nao Hibino 6-1, 6-1 in just 55 minutes.
Up next for the third seed is Monica Puig of Puerto Rico.
There was also a win for two-time Wimbledon champion Petra Kvitova over Danish flag-bearer Caroline Wozniacki 6-2, 6-4.
US seventh seed Madison Keys came out on top in a three-hour duel against Kristina Mladenovic of France 7-5, 6-7 (4/7), 7-6 (7/5).
Martina Hingis, playing in her first Olympics in 20 years, teamed up with Timea Bacsinszky to reach the women's doubles second round.
The Swiss pair defeated Coco Vandeweghe and Bethanie Mattek-Sands of the United States 6-4, 6-4.
Later Monday, Japan's Kei Nishikori meets Australia's John Millman who created history in the first round when he recorded the first 'double bagel' 6-0, 6-0 win in Olympic history.
Olympic Games tennis results on Monday:
Juan Martn Del Potro (ARG) bt Joao Sousa (POR) 6-3, 1-6, 6-3
Taro Daniel (JPN) bt Kyle Edmund (GBR) 6-4, 7-5
Roberto Bautista Agut (ESP) bt Paolo Lorenzi (ITA) 7-6 (7/2), 6-2
Gilles Muller (LUX) bt Jo-Wilfried Tsonga (FRA) 6-4, 6-3
Gael Monfils (FRA) bt Rogerio Dutra Silva (BRA) 6-2, 6-4
Marin Cilic (CRO) bt Radu Albot (MDA) 6-3, 6-4
Andrej Martin (SVK) bt Philipp Kohlschreiber (GER) - walkover
Kei Nishikori (JPN) bt John Millman (AUS) 7-6 (7/4), 6-4
Serena Williams (USA) bt Alize Cornet (FRA) 7-6 (7/5), 6-2
Elina Svitolina (UKR) bt Heather Watson (GBR) 6-3, 1-6, 6-3
Petra Kvitova (CZE) bt Caroline Wozniacki (DEN) 6-2, 6-4
Ekaterina Makarova (RUS) bt Anna Karolna Schmiedlov (SVK) 3-6, 6-4, 6-2
Garbie Muguruza (ESP) bt Nao Hibino (JPN) 6-1, 6-1
Mnica Puig (PUR) bt Anastasia Pavlyuchenkova (RUS) 6-3, 6-2
Laura Siegemund (GER) bt Zhang Shuai (CHN) 6-2, 6-4
Kirsten Flipkens (BEL) bt Lucie Safarova (CZE) 6-4, retired
Madison Keys (USA) bt Kristina Mladenovic (FRA) 7-5, 6-7 (4/7), 7-6 (7/5)
Carla Suarez (ESP) bt Ana Konjuh (CRO) 7-6 (7/5), 6-3
Sara Errani (ITA) bt Barbora Strycova (CZE) 6-2, 6-2
Darya Kasatkina (RUS) bt Zheng Saisai (CHN) 6-1, 6-4
Svetlana Kuznetsova (RUS) bt Monica Niculescu (ROM) - walkover
Johanna Konta (GBR) bt Caroline Garcia (FRA) 6-2, 6-3
Samantha Stosur (AUS) bt Misaki Doi (JPN) 6-3, 6-4
Angelique Kerber (GER) bt Eugnie Bouchard (CAN) 6-4, 6-2