That day the two had staged an all-out Grand Slam semi final war on Court Central. The stakes were high - at the end of the dual stood a coveted berth in the Roland Garros singles final, which Pierce today won in straight sets, becoming the first Frenchwoman in 33 years to claim the crown.
During that tense match against Hingis, emotions ran hot, dreams were shattered (Hingis is yet to win Roland Garros) and expectations were raised (Pierce was a national hero).
Which is why coming back out onto court to play doubles with each other the next day might have been a definite stretch of the friendship for Pierce and Hingis.
Stretch of the friendship? Maybe not. But there was no question that their singles semi final did place a strain on the pair during their first set downfall against Frenchwomen Alexandra Fusai and Nathalie Tauziat on Friday. They lost that first set 2-6, but recovered to win in three sets and move into their second consecutive Grand Slam doubles final on Sunday.
Said the Swiss Miss: "It was probably difficult for me, that maybe I'm disappointed after yesterday. Mary is already thinking about the next match. Once we started playing our game, we were so much better. We knew it was going to be hard to come out here today for both of us.
"I just try to give the best, and support Mary because she's got the final."
Continued Pierce, matter-of-factly: "Sometimes you have to play against friends or your partner in doubles. We understand, both of us, that we are going to play against one another. We have to forget about those relations. I want to win. She wants to win. There is nothing personal. We have to be professional."
And despite the obvious misgivings of playing with another high profile singles partner, the Frenchwoman has made it clear that she won't be scouring the 'Doubles' section of the classifieds anytime soon: "No, not at all. It is not the first time we are playing against each other in singles. We play doubles afterwards."
And, upon reaching the final, Pierce is adamant that she never even considered withdrawing from the doubles.
"No, not at all. Martina asked me how I was feeling about playing the doubles, you know to be ready for the finals. It never really entered my mind that I wasn't going to play unless I couldn't walk," laughed Pierce.
"I just have so much fun playing with Martina. I think we have a great chance to do well here. When I start a tournament with somebody, I just want to commit with them and go all the way to the end."
The third-seeded Hingis/Pierce combo like their chances against the No10 seeds Virginia Ruano Pascual and Paola Suarez in the Roland Garros women's doubles final on Sunday afternoon.
"I think we have a pretty good chance now in the finals......Singles...you know she's my partner, so I wish her all the best. She's going to be more happy for the doubles final I hope, if she doesn't celebrate too much.
Hingis is particularly fond of the crowd's warm reaction to her when she is on the same side of the net as Pierce: "When I was with Mary on court, I had them behind me all the time."
Since teaming up earlier this year Pierce and Hingis have developed into a formidable duo - reaching three finals (Sydney, Australian Open and Japan) and winning one (Japan). Hingis has already won one Roland Garros doubles title (in 1998 with Jana Novotna). The Swiss Miss has one of the best doubles games in the business (she's won seven Grand Slam doubles titles already), and also reached the doubles final here in 1998, the semis in 1997 and the quarters in 1996.
Teaming with Pierce, the newly crowned Roland Garros singles champion, looks like a surefire way to reach a Grand Slam final.
"We just both try to support each other. Sometimes she tells me things, sometimes I do. We don't come in as much as maybe you would on a hard court. You just have to adjust," said Hingis.
"It's what makes us such a good team, especially at this tournament, that we're able to adapt."