England, holders Wales and Scotland opened their Rugby World Cup Sevens campaigns with wins at the Luzhniki Stadium in Moscow on Friday.
John Brake ran in a brace of tries and Tom Mitchell also touched down as England notched a 21-7 victory over Portugal in Pool F, with Christian Lewis-Pratt adding the extras on each occasion.
In sweltering conditions that were nearing 40 degrees Celsius, England took a little time to settle in before Dan Norton's unselfish offload put Brake through to score the opening try.
Portugal soon hit back and a quick tap from Miguel Lucus saw him barge his way over the line to notch a converted try to level the scores 7-7 at the break.
England's superior fitness told in the second-half as Ben Ryan's men pulled away, with Brake finding space to run in his second try and Mitchell rounding off the victory following Mat Turner's offload.
England next play Hong Kong on Saturday before what should be the Group F decider against Argentina - who beat Hong Kong 47-7 - later the same day.
Welcoming the victory, head coach Ryan said: "It's great to get day one out of the way with a win under our belt. Match days with just one game are long hard days when you know you have just got to empty the tank.
"Portugal played well and they were tough in the breakdown. We have certainly got room for improvement and I think if we had done two or three things better today then we would have won by a bigger margin.
"Hong Kong are next up for us and we'll be focusing all our energies now on that game. It is tough in these humid conditions and the pitch was cutting up a little too, but actually the boys came off the pitch feeling fresh and raring to go again."
Holders Wales began their defence with a comfortable 33-5 victory over Uruguay in Pool E, with Chris Knight scoring an early try.
Adam Warren also touched down and Gareth Davies converted before Knight added his second try and Davies converted.
Felipe Berchesi pulled a try back for Uruguay before the break but further tries from James Davies and Alex Webber saw out the win.
Scotland survived a late fightback from Japan to open their account with a 19-17 victory in Pool B.
Tries from Chris Dean, Andrew Turnbull and Michael Fedo, with two conversions by Colin Gregor, saw Scotland race to a 19-0 lead.
But Japan hit back, with tries from Lote Tuqiri and Shota Emi and a conversion from Katsuyuki Sakai.
Kosuke Hashino then touched down to leave Japan just two points behind but Sakai failed to convert as Scotland hung on for the win.