The Saviour's Day performer was playing in front of several thousand fans at the Killarney's INEC in Ireland before he takes his latest show to the UK.
Sir Cliff met fans before the performance but ignored questions about the police inquiry into allegations of sexual abuse.
It was his first stage appearance since the allegations emerged over a year ago.
The accusation is said to have taken place at an event with the evangelist Billy Graham in 1985.
Sir Cliff previously said the claims against him were "absurd and untrue" and he had "never, in my life, assaulted anyone".
The singer was interviewed under caution but he has not been arrested and no charges have been brought.
Fans in Killarney jumped to his defence.
Joan Batten, from Penmaenmawr in north Wales, was in the same church as Sir Cliff, St Paul's in Finchley, north London, for six years from the late 1960s.
"These people who laugh about him have not met him or seen him in concert," she said.
Ms Batten, who played badminton with Sir Cliff and attended parties and dinners with him, said: "He's a complete and true gentleman.
"There's absolutely no other side to him, what you see is what you get.
"I've never seen him be nasty to anyone."
Bernie Downes from Oxford, first saw Sir Cliff perform in 1969, and followed it up by attending more than 200 shows.
"I'm really happy that Cliff is doing another tour to celebrate his 75th birthday and everything else," she said.
"He's had a lot of problems over this last year with people he knows, close friends, Cilla Black's death and things in his personal life."
"It all started with that Jimmy Savile."
Betty Carroll, from Liverpool, first saw Sir Cliff in the city's Empire club in 1959, but did not see him again until 1986 when she began travelling worldwide to catch his shows.
"Someone is trying to get him somewhere," she said about the allegations.
"I don't believe a word of it."
"John Lennon once said something horrible about him and I said to him 'if I was you I'd hit him' and he said it's his opinion and everyone's entitled to that."
