Barca could have won by a greater margin in the end, but striker David Villa was unusually wasteful in front of goal and failed to score against his former club.
Nevertheless, Guardiola backed his summer signing to come good.
"He has scored so many goals in his career," he said. "He has the will and the determination to be a big success and he's working very hard - I'm pleased with him."
And Guardiola was even more pleased with his side's comeback.
"It was an extraordinary performance in the second half," he said. "In the first half we were outplayed, we were too slow, we were beaten to the second ball and we didn't close down well enough, but I was delighted with how we came out in the second half."
Until then, Barca had looked lacklustre and found themselves behind at the break.
The Catalans had only won one of their three league games at the Nou Camp prior to this one, strangely struggling to break down inferior sides in those games.
But Guardiola says he was unconcerned - even when his side trailed at the break.
"We could have lost today," he said. "Valencia are a fantastic team with great players and they were on top, but I would always prefer to play at home - I know what we can do here and I knew we could turn it around."