Pool B rivals Great Britain, meanwhile, will join them in the last eight having scored 58 unanswered points to record back-to-back victories as sevens’ second appearance at the Games began in style.
In Pool A, New Zealand booked a quarter-final spot with wins over the Republic of Korea and Argentina, while South Africa and the USA lead the way in Pool C having also made a perfect start to the tournament.
Fiji and Great Britain lead Pool B
It took Fiji just 20 seconds to open the scoring in the opening match of the men’s tournament, as Jiuta Wainiqolo crossed the whitewash.
Japan captain Chihito Matsui hit back within two minutes, and after Iosefo Masikau Baleiwairiki had scored an unconverted try for the Fijians, Lote Tuqiri touched down as the hooter sounded to help give the home side a 14-12 half-time lead.
Japan stretched their advantage early in the second period as Kameli Raravou Latianara Soejima powered down the left wing to score.
Soejima’s intervention meant Fiji trailed by seven points, but the Rio 2016 gold medallists turned the tables with two tries in as many minutes from Waisea Nacuqu to win the match 24-19.
Gareth Baber’s side followed up that victory with a second against Canada in the afternoon session, but the defending champions were made to work hard for it.
Fiji built a 14-0 lead through tries from Napolioni Bolaca and Wainiqolo, but Nathan Hirayama finished a flowing Canadian move on the stroke of halt-time to score his country’s first Olympic try.
Canada spent much of the second half inside opposition territory, but Justin Douglas’ try was sandwiched between break away efforts for Aminiasi Tuimaba and Asaeli Tuivuaka which sealed a 28-14 win for Fiji.
It was a second defeat in two matches for Canada, who started their campaign with a 24-0 loss to Great Britain. Dan Norton opened the scoring at the end of a cagey first half of that match, and then added a second within seconds of the start of the second period.
Tries from Ross McCann and Robbie Fergusson in the final two minutes of the match put some gloss on the win for Great Britain.
Harry Glover was the star of Great Britain’s second match of day one, as Tony Roques’ side recorded their biggest ever Olympic win, 34-0 against hosts Japan.
Glover set up his side’s opening two tries, scored by Dan Bibby and Tom Mitchell, and then crossed for the third himself.
He again provided the assist as Ben Harris scored Great Britain’s fourth try before Ethan Waddleton and Alex Davis put the seal on another impressive win.
New Zealand impress in Pool A
Andrew Knewstubb got the All Blacks Sevens on the scoreboard with a converted try before Jeong Yeon Sik found space down the right wing to score and cut the Korean deficit to two points.
Tim Mikkelson got his first try of the Games at the end of the first half, and shortly after the restart Scott Curry was called on to deny another powerful run by Jeong.
New Zealand were awarded a penalty try when Yong Heung Chang was sent to the sin-bin for a deliberate knock-on and went on to cross the whitewash another five times before the end as Mikkelson, William Warbrick (twice), Etene Nanai-Seturo and Ngarohi McGarvey-Black all touched down.
The All Blacks Sevens made it two out of two in the afternoon session, holding off swathes of Argentine pressure to win 35-14.
Youth Olympic Games gold medallist Marcos Moneta scored an early try to give Argentina a 7-0 lead, before New Zealand hit back through McGarvey-Black and Sione Molia.
Argentina again struck early in the second period as Luciano Gonzalez crossed the whitewash to help level the score at 14-14.
But, that was as good as it got for the South Americans as Joe Webber, Mikkelson and Warbrick all touched down. No Kiwi has scored more Olympic tries than co-captain Mikkelson’s four.
Earlier on Monday, Argentina secured an impressive 29-19 defeat of Australia. The South Americans raced into a 24-0 half-time lead at Tokyo Stadium as Lucio Cinti, Matías Osadczuk, Moneta and Ignacio Mendy all breached the Australian defence.
Tim Walsh’s side hit back in the second period, narrowing the deficit to five points as Josh Turner (twice) and Samu Kerevi crossed the whitewash.
But, as Australia went in search of a potentially match-winning try, the ball broke to Lautaro Bazan Velez and he raced away to put the seal on an Argentine victory.
South Africa and USA unbeaten in Pool C
South Africa, meanwhile, scored five tries to beat Ireland 33-14 and kick-off their Pool C campaign with victory on day one.
Zain Davids opened the scoring for the Blitzboks before Impi Visser added a second try with less than six minutes gone.
Gavin Mullin got Ireland on the board before the break, but it was South Africa who struck first in the second half as Justin Geduld rose highest to claim a cross-field kick and dot down.
Terry Kennedy grabbed his first Olympic try to give Ireland hope of a comeback, but the Blitzboks made sure of victory with an expertly-taken Chris Dry effort and a late score from Stedman Gans.
The Blitzboks raced into a 14-0 lead in the final match of the day, against Kenya, but were made to withstand serious pressure in the second period to hold on to the win.
Collins Injera scored for Kenya on the stroke of half-time but despite their best efforts in the second period, they were unable to breach the South African defence again and lost 14-5.
Defeat was Kenya’s second of the day after they slipped to an agonising 19-14 loss against the USA.
Tries from Carlin Isles and Martin Iosefo had given the USA a 12-0 advantage, but Kenya hit back to lead by two points after Collins Injera and Jeff Oluoch touched down.
Veteran Willy Ambaka thought he had put a seal on a Kenyan win, but he was judged to have lost the ball forward and the USA went up the other end to win a pulsating match 19-14 as captain Madison Hughes scored.
Hughes was again on the scoresheet as the USA secured a second win of day one in the penultimate match of the afternoon session, beating Ireland 19-17.
The USA captain won the race to his own kick through to score his side’s second try of the match and put them 12-0 in front.
Ireland replied with tries either side of the half-time break, scored by Hugo Lennox and Harry McNulty, but their hopes of victory appeared to be ended when Steve Tomasin went over for the USA. There was still time, however, for Foster Horan to score but it proved too late to prevent defeat.