Rondon was brought to Newcastle from West Bromwich Albion in the summer, and he initially struggled for fitness.
However, the striker was brought back to start against Watford, as Newcastle picked up a 1-0 victory.
Benitez had planned to play the target-man for around an hour, but Newcastle picked up three injuries in the second-half, which meant Rondon had to play the entire match.
Benitez predicted that Rondon would be fatigued this week, due to his exertions last Saturday.
But the Spanish boss claims that Rondon has been surprisingly good in training.
"I think it will benefit him to have played for 90 minutes, even if it isn't what we were planning [before the Watford game],” Benitez said.
"His match fitness is still not ideal, and maybe we were expecting him to play just 70 minutes, or something like that, against Watford.
"He had to play 90 minutes after the injuries we had, he was working very hard and giving us something different. Then, during the week, he has been training - and, even though we thought he would be tired, he was doing really, really well.
"With all that, I think it was only a good thing for him to have played 90 minutes last week, and hopefully we see that on Saturday.”
Newcastle’s win over Watford was their first of the season, and took them out of the relegation zone.
Benitez’s side are next in action at the weekend, when they take on Bournemouth.