The game was only five minutes old when the Dutch defender, signed from FC Groningen in the summer for around £2.5million, picked the ball up in his own half and drove towards the Saints box.
The 22-year-old left a string of blue shirts trailing in his wake before he knocked it past Perth goalkeeper Alan Mannus from around 10 yards out.
The goal was ultimately enough to stretch the Hoops' unbeaten run in the league to 17 games before their trip to Inverness on Sunday and the Hoops boss insisted it deserved special praise.
"If we'd dropped points we probably would not have been talking about Virgil's goal," said Lennon.
"So I'm glad we are because it was an unbelievable piece of individual brilliance. He certainly lit up the game.
"I'm not expecting him to do that all the time but he's an exceptional player, a great defender and he's certainly made us better.
"He's added the physical presence and height we've been missing. He's been a good piece of business for us."
Van Dijk was pleased with his effort, saying: "It was a good run and a good finish as well, so I am very happy with the goal.
"I have tried it in other games but today I finally did it."
Lennon claimed his side should have had made things easier for themselves.
"It was closer than it should have been after the first half," he said.
"I thought we controlled the game on a difficult pitch. But we have to put teams away.
"At 1-0 you give teams encouragement. But we've never had it easy here. St Johnstone came out for 15-20 minutes in the second half and were full of running and desire to get back into the game.
"But we saw it off and in the last 20 minutes we were okay again."
St Johnstone boss Tommy Wright claimed his side should have been awarded a penalty after the break when Van Dijk appeared to block the run of striker Stevie May in the box but referee Craig Thomson decided to wave play on.
The Northern Irishman said: "I thought it was a penalty at the time and I've seen it since.
"Nothing has changed my mind. Anywhere else on the pitch it's a free-kick so it should have been a penalty.
"There were some bookings we felt were not bookings for us.
"Craig is a good referee and I thought he had a good game, but you always have decisions you feel go against you.
"I think we deserved to take something. Celtic created more chances but we contributed to a good game in the second half.
"In games like this you need a bit of luck and a decision here and there to go for you. We didn't get that today.
"But overall I'm pleased, we created a few chances against the best team in the country.
"If we play like that most weeks we'll pick up points."
Lennon rejected the penalty claim, saying: "I thought he just stood up and was strong, which is what we had to do at times."