Speedster Marco Moneta fired five-man Argentina to a nail-biting 19-14 victory over South Africa Tuesday to set up a rugby sevens semi-final against defending Olympic champions Fiji.
Powerhouses New Zealand, long the dominant force in the abbreviated game, will take on Britain in the second last-four clash on Wednesday.
Selvyn Davids opened the scoring for Rio bronze medallists South Africa at the Tokyo Stadium, but on the next play was taken out high by Gastón Revol.
The veteran Argentine was left sobbing on the touchlines after he was rightly shown a red card.
Moneta, however, scored two magnificent solo tries against the run of play to put Los Pumas 14-7 up at half-time.
First, he span into space down the left wing and ran in from 60 metres before then gathering his own kick ahead for a memorable second. Santiago Álvarez added a third, but more drama was to ensue.
Lautaro Bazan Velez was shown yellow in a move that saw the Boks awarded a penalty try with 20 seconds to play -- enough time to change a game of high-octane sevens on its head.
But Argentina, now down to five, claimed the restart and the ball was booted into the stands in delight.
"It was a historic match! It was crazy," said Moneta.
Skipper Álvarez added: "We came looking for history. We got through that quarter-final that is so difficult for us. We are very excited and very happy for everything we did on the pitch."
Los Pumas will face Fiji on Wednesday, the South Pacific islanders made to work hard for a 19-0 victory over Australia.
Once again it was playmaker Jerry Tuwai who was key for Fiji, scoring a vital double and marshalling an effective sweeper system that fired a hard-hitting defence that rarely allowed the Wallabies out of their own 22m area.
Aminiasi Tuiamba scored a late third for a dominant Fiji side at an empty stadium in temperatures of 27 degrees Celsius (81F) and 80% humidity after earlier rain showers.
Britain fight back
Britain, who claimed silver in Rio after losing 43-7 to Fiji in the final, had to dig deep for a 26-21 victory over the United States, for whom Danny Barrett and Perry Baker (two) scored quickfire tries.
But Ollie Lindsay-Hague clawed one back at the half-time hooter and Ben Harris opened up the scoring in the second half for Team GB after American Steve Tomasin had seen yellow for a deliberate knock-down.
Britain made their numerical advantage pay, Alex Davis stepping through at close range for a converted try that levelled the scores. It was left for veteran Dan Norton to sprint in from halfway to hand his team the decisive lead for the first time with two minutes to play.
"It's pretty unreal when you're down like that, we could have been down and out at half-time, but the score before half-time and resilience in the second half is what we're all about," said Britain's Robbie Fergusson.
The Kiwis took almost five minutes to crack a resolute Canadian defence in their quarter-final, Andrew Knewstubb jinking over to ease the pressure.
Scott Curry doubled the score before Knewstubb got his second against a tiring Canada team, for whom Pat Kay and Harry Jones had two late consolation tries in the 21-10 defeat.
"You can't win the Olympics today, but you can certainly get knocked out," said New Zealand coach Clark Laidlaw, adding that atonement for their Rio quarter-final exit was not on their minds.
"Sevens is such a fickle game that the last game doesn't really influence the next game, let alone five years ago. We are just really encouraged around how we are playing. Still being in the tournament is key at this stage."
Hosts Japan were left to battle it out with South Korea for 11-12th place after losing 21-7 to Kenya, who will take on Ireland, 31-0 victors over the Koreans, for 9-10th place.