The 38-year-old was the Capital side’s best player as he was called into action throughout the 3-2 loss at Parkhead in the Premier Sports Cup clash.
Celtic had 36 shots with 11 on target, making it Gordon's busiest game in the last six years.
The goalkeeper showed his shot-stopping quality with a wide range of saves. His heroics allowed Hearts to stay in the tie despite struggling to get a foothold in the game.
“Craig was exceptional again,” Neilson said. “He makes big saves. But that’s what he does.
"In my opinion he’s the best goalie in Scotland. He showed again today that he’s a top, top keeper.”
Gordon will be hoping to be called up by Steve Clarke for the country’s World Cup qualifiers next month.
Scotland face a triple header against Euro 2020 semi-finalists Denmark, Moldova and Austria.
David Marshall, who was Clarke’s No.1 at this summer’s tournament, has dropped down the pecking order at Derby County and finds himself third choice.
Neilson hopes Gordon has done enough to convince Clarke to be the starting goalkeeper for the Denmark clash in Copenhagen at the start of September.
“I would expect him to get back in it,” he said. “I don’t see anybody who is doing better than him just now.
"He will be in the next squad and then it is up to Steve to decide if he is No.1 or not.”
Meanwhile, Neilson revealed why Andy Halliday was substituted at half-time of the Celtic game with Hearts trailing 2-0.
The midfielder had picked up a knock, while the manager wanted to tweak the shape to try and gain a foothold in the match.
Halliday is expected to be fit for the cinch Premiership fixture with Aberdeen at Tynecastle Park on Sunday.
“He has got an Achilles problem,” Neilson said.
"It was partially to change the shape, it was partially because he had a wee niggle in his ankle.
"He will be fine for next weekend. He should be training in the next couple of days.”