1132 GMT January 22, 2018
An impressive performance at the Etihad Stadium from the Robins – who had beaten Watford, Stoke, Crystal Palace and Manchester United en route to the last four – saw the Bristol side take a shock lead through Bobby Reid's 44th-minute penalty, PA Sport reported.
Kevin De Bruyne equalized in the 55th minute and the quadruple-chasing, runaway Premier League leader snatched victory on the night via substitute Sergio Aguero's stoppage-time header.
Guardiola said, "It was a nice game, beautiful game, and all my credit to Bristol City.
"We knew that (it would be a tough game) because you cannot knock out four teams from the Premier League without (being) well organized and having nice players to watch."
When asked what he had said to opposite number Lee Johnson at the end of the game, Guardiola said, "Big congratulations. He came here to try to play.
"They arrived, they created chances. They are up in the Championship (Johnson's side are fourth), and I have a lot of respect for what they have done."
While the host certainly did not produce one of its finest performances, Guardiola was also keen to laud the way his side reacted to the setback of falling behind.
"It is fantastic. I am a lucky guy to train the players I have," he said.
"Always semifinals are tough, and 1-0 down, how we reacted in that situation... I don't know what is going to happen at the end of the season, but my respect for these professionals, with this amazing schedule – every single game, they do absolutely everything that they have.
"I think Manchester City fans here and around the world have to be so proud. Because it is so complicated what they have done – to, mentally, every day stay there, and we did it again."
Guardiola's men also came back from 1-0 down at halftime to win on Saturday as they defeated Burnley 4-1 in the FA Cup, and he added, "Without that spirit you can't win trophies in any competition.
"We try and try and try until the last minute.
"That is going to be essential in competitions like the Champions League."