Southampton-based Waterfield and teammate Daley showed signs of rustiness in their first competition since finishing sixth at last July's World Championships as they relied on an impressive last dive to win through to the 12-team final.
The duo's 18-month partnership has been undermined by injury and other factors, with Waterfield only returning today after two months out with side and back problems while a thumb complaint forced Daley to miss last month's British National Cup.
They did get some much-needed practice at a camp in Southend last week and Waterfield believes today will only speed their return to peak form ahead of the Olympics.
"When you know you haven't had as good a preparation as you want it's always a negative in your mind," he said.
"Really I've only just started doing my list again, so it's tough in front of a crowd with a lot of expectation.
"We've done the job. We're through to the final. We'll try and enjoy it and put some pressure on the others.
"We need to do competitions and be competition fit. Now that we've got over our injuries we can do some more competitions and some training and peak when we need to."
Daley agrees there is room for improvement.
"It wasn't our best performance by any means," he said.
"But the thought that we dived like that and finished sixth and qualified for the final is comforting.
"We know that we have to step it up a lot in the final."
The pair had been 10th going into their final dive before attracting their best score for their back two-and-a-half somersault two-and-a-half twist.
"We had to make sure we pulled it out of the bag," Daley said. "It was our best scoring dive. Going into the last dive and you hear the crowd roaring like that it does give you an extra adrenaline buzz to do it well."