Team USA's Madison Hughes made amends for an early missed conversion by scoring a late match-winning try as the Americans began their Olympics with a 19-14 defeat of Kenya at the Tokyo Stadium on Sunday.
Coach Mike Friday's men led 12-0 on tries from Carlin Isles and Martin Iosefu, but found themselves down 14-12 with less than a minute to play in Chofu.
That's because Kenya's Carlos Injera scored a try before halftime and Jeffrey Oluoch did the same after the break, with Eden Kochieng Agero succeeding with both of his conversions.
But Hughes got the ball over the line and onto the ground 29 seconds before time and Stephen Tomasin converted to put the final score on the board and get the Americans off to a winning start.
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South Africa, New Zealand, Great Britain all cruise
Earlier, world No. 1 South Africa took an early 14-0 lead and never looked back in opening its Olympics with a 33-14 defeat of Ireland in men's rugby pool play on Sunday.
The Pool C and tournament favorites got tries from five different athletes and Selvyn Davids hit on four-of-five conversion attempts in the win.
Argentina built a 24-0 halftime lead that shrank to five before a late Lautaro Bazan Velez try supplied the South Americans a 29-19 win over Australia
Fiji came back from a 19-12 deficit to surprise Japan 24-19, Waisea Nacuqu accounting for the final seven points.
Great Britain blanked Canada 24-0 and New Zealand hammered South Korea 50-5, four players recording nine or more points in the win.