Tonga forward Nasi Manu admitted he was full of emotion, after playing his first game in 13 months, since recovered from testicular cancer.
Manu came off the bench in the 57th minute of Tonga's Rugby World Cup opener against England, which the latter won 35-3 in Sapporo on Sunday.
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Last year, the former Highlanders captain had surgery to remove an abnormal growth, then endured months of chemotherapy, before receiving the all-clear to return earlier this year.
Manu was scheduled to play for Tonga in the Pacific Nations Cup, but a pectoral injury kept him out of action for that tournament and the 92-7 hammering from the All Blacks.
The occasion was more special as the 31-year-old's first appearance at a World Cup, while his wife and daughter watched from the stands.
"The whole day has been very difficult for me, just controlling the nerves," said Manu. "I couldn't sleep last night, I just got too excited.
"I was telling my wife that I didn't know what to do. I packed my bags five times.
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"After five minutes on the field, I felt my legs were gone. No fitness can prepare you for that.
"I don't know what Toutai [Tongan coach Toutai Kefu] has planned for me for the rest of the tournament, but the other guys are playing so well.
"I have achieved my dream of playing in a World Cup, whatever happens, and I have so many people I can thank for getting me here. I can't say names, because I am afraid I will miss some out."
Tonga coach Kefu said Manu's return was inspirational for the rest of the squad.
"It's been an emotional week for Nasi. We tried to lighten his load in terms of media and sponsorship commitments, but we all knew this was important for him.
"I just had a chat with him, and he said he was bloody tired and needs more game time. His lungs were gone, but I reassured him and said, 'you're lucky to be on the field'.
"Knowing him, he is a bloody competitive person and a bloody good player."
Despite losing to England, Kefu was pleased with the progress of his team and felt quietly confident ahead of their next match against Argentina on Saturday.
"We didn't play well against the All Blacks and caught them on a bloody good day, so we just needed to talk about a few things. The good thing is it meant we had to put ourselves under the magnifying glass.
"Today went much better - we had a gameplan, which we executed. They are a good team, they squeezed us in the first half and we couldn't get into their 30 to throw any punches.
"We need to keep chipping away at our core skills under pressure. We are getting better, but there are some opportunities we are not taking advantage of.
"We stayed in the game really well, they just got away from us in the second half."
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