The Swansea winger marked his first competitive international start with a fifth-minute strike as Wales got their Euro 2020 qualifying campaign off to a winning start.
James, who has established a growing reputation in the Sky Bet Championship this season, robbed Slovakia right-back Peter Pekarik on the edge of the area before drilling a shot past Newcastle goalkeeper Martin Dubravka as Wales triumphed 1-0.
“He has brought his club form on to the international stage,” Giggs said.
“I am delighted because his overall game was fantastic, and to top it with a goal was great. He was just a threat all day.
“He is a talent, and when you have got that raw pace you are a threat at any level.
“As a winger, you then have to develop the other parts of the game, which I feel that he is doing. He just needs to carry on doing what he’s doing for Swansea, it’s as simple as that.”
Wales had to withstand considerable spells of second-half pressure from Slovakia to preserve their lead, and Giggs was delighted to collect maximum points.
“It was the perfect start really,” he added. “A clean sheet and three points.
“There was a bit of pressure on us. I tried to play it down beforehand, but you can’t hide from the fact that the other teams have played and that Croatia and Slovakia got three points.
“It was nervy at the end. We didn’t really punish Slovakia enough in the first half, and you wonder if that will come back to haunt you.
“Second half we were under pressure and we had to defend.
“A couple of times we could have kept the ball better and made better decisions. We will learn from it and hopefully it will stand us in good stead going forward.”
Giggs dropped captain Ashley Williams to the bench, with Gareth Bale taking over as skipper for only a second time in his international career.
Asked about Williams’ omission, Giggs said: “With the advantage we had physically, I wanted every player to be playing regularly. That was the only reason.
“He came on, saw us home and is part of the plans going forward.
“Ash is still the captain. You never know from camp to camp who’s playing regularly, who’s not, who is injured.
“You are never going to take it well, and you don’t want players to take it well. He didn’t sulk.”
Wales resume qualifying action away from home against World Cup finalists Croatia and Hungary in June.
“It’s not going to be easy because it is two away games,” said Giggs, who confirmed that Wales would prepare for those fixtures with a six-day training camp in Portugal.
“We saw the other night when Hungary were unlucky (against Slovakia), and the quality of Croatia – everyone recognises they are favourites to win the group.”
Slovakia manager Pavel Hapal was disappointed that his team failed to collect a point from their second pool game.
“It was a very interesting match,” he said.
“We were very good in the second half, but we made a lot of mistakes in the first half and Wales gained a lot from their pressing game.
“We pushed our opponents in the 90 minutes and we had a few chances. I think we could have got a point today.”