Argentina took a surprise 2-0 lead in their Davis Cup semi-final against Great Britain after Juan Martin del Potra beat Andy Murray in a five-set thriller in Glasgow.
Del Potro won 6-4 5-7 6-7 (5-7) 6-3 6-4 after more than five hours on court against the Wimbledon champion.
The pair also faced each other during a four-hour Olympic final lost month, with Murray coming out on top on that occasion.
"I won but I still remember the Olympic final," Del Potro told BBC Sport. "This is very important to me and my team and we are looking to reach another final in the Davis Cup.
"Against Andy you never know when the match will finish. He is a dangerous player, a fighter and great champion. In end I played good forehands and good serves and that was key."
After taking the first set, Del Potro found himself on the receiving end in sets two and three, but the 27-year-old was able to turn the tables, claiming the decisive breaks in sets four and five to give Argentina a 1-0 lead.
Del Potro, who recently returned after a lengthy injury lay-off, hit 26 forehand winners and broke serve six times in all.
"I am so happy to be playing tennis again after three surgeries," he added.
"This kind of moment was what I was missing at home and I always play good in Great Britain, and here I played great, so it is a good place for my tennis."
It didn't get much better for Great Britain from there, as Guido Pella fought back from a set down to defeat Kyle Edmund 6-7 (5-7) 6-4, 6-3, 6-2 and give Argentina a 2-1 lead.
The defending champions will now have to win all three remaining matches in order to come back in this tie.
In the other semi-final, France and Croatia are locked at 1-1 going into Saturday's action.
Richard Gasquet gave the visiting French a 1-0 lead after beating Borna Coric 6-2, 7-6 (7-5), 6-1.
But Maric Cilic hit back for Croatia to level the scores, edging Lucas Pouille 6-1, 7-6 (7-4), 2-6, 6-2.