Donnelly won a unanimous points decision over a wild-swinging Algerian, Zohir Kedache, winning all three rounds and the second round 10-8 on one judge’s card.
If there was a problem in the camp caused by the positive doping test that team-mate O’Reilly gave before leaving Dublin, Donnelly disguised it with the cool control in the ring and his excitement in the mixed zone after it.
He was loving every minute of his first Olympic Games. “It’s brilliant, the buzz just keeps picking up,” said the Ballymena welterweight. He was keener to say how he had met Andy Murray and Michael Phelps than anything about his suspended team-mate.
Donnelly has a good idea how O’Reilly must be feeling. He was sent home early from the Commonwealth Games in Delhi in 2010 for breaking Northern Ireland team rules on drinking in the Athletes Village.
He was so embarrassed about it he did not box for two years and started again only after apologising to his club in Ballymena for bringing it into disrepute.
Yesterday the eighth seed showed no sign of suffering collateral damage from the drama that overtook the Irish team two days earlier when news of O’Reilly’s positive test came as team officials were watching the draw in a Rio auditorium.
“I’m very happy with that. There’s always pressure before a first fight. I was very nervous beforehand, I always am, but you have to handle it and I handled it very well,” he said.
“I haven’t put on a great performance yet. I will get better. I can go all the way. I have to believe that, believe in myself and keep pushing.”
His second round fight on Thursday will be against a Mongolian Tuvshinbat Byamba, who will be more of a handful than yester day’s opponent.
He was far too good in the bout before Donnelly’s against Argentine Alberto Palmetta, winning every round.
The Irish boxers seemed in similarly good spirits, Paddy Barnes and Michael Conlan taking a gentle swing at the absent golfer Rory McIlroy on Twitter. McIlroy responded wishing them good luck.
“If your boxing is as good as your tweeting it should be two guaranteed gold medals,” he tweeted.
“Good to see you have a sense of humour Rory, we’re all friends here,” replied Conlan, the bantamweight seeded first here and not in action until next Sunday.
Team coach Eddie Bolger confirmed that reading of the mood in the camp.
“It hasn’t affected anybody. It’s an individual sport. They are seven individuals.”
O’Reilly is in isolation within the Olympic Village, spared the indignity so far of Greek and Cypriot competitors who tested positive before the Games and were expelled immediately from the Village.
O’Reilly has been moved from his shared room among the other seven boxers and their coaches, according to team manager Joe Hennigan, but not humiliated yet with an air ticket home.
He and the officials are waiting upon a hearing of the Irish Anti-Doping Disciplinary Panel which O’Reilly has asked to consider his case.
Nobody within the team or in Ireland is confirming the substance he has tested positive but given he has only five more days before his scheduled first bout he will do well to gather sufficient evidence to clear himself.
He may claim it was consumed inadvertently or that a natural food or supplement had been contaminated but the World Anti Doping Agency rules demand an athlete prove his innocence once a test is positive.
Unless he can convinced the appeal panel probably in a conference call of his innocence. O’Reilly faces the prospect of being recorded in Irish Olympic history as the first athlete ever to be sent home from a Games because of a doping charge.
When asked about the O’Reilly saga, Donnelly replied: “It’s just old news for us now, we each have to concentrate on our own game.
"What happens, happens. We’re all concentrating on our own games and doesn’t affect us at all really. We’re a strong team and we know how to deal with these situations. Team morale is fantastic, it’s great.”