The young striker admitted netting against the Jambos' arch-rivals was a dream come true.
But Laszlo urged him not to get carried away with his heroics, telling Hearts News Today: "The player must not fly too high after yesterday.
"He must keep his feet on the ground and keep working hard.
"We have another very heavy opponent coming up in Aberdeen on Saturday and we will wait and see what happens with the team for that game.
"It was a fantastic goal from the young player but he cannot afford to get carried away."
Smith only started after fellow youngster Scott Robinson cried off injured on Saturday.
The under-19 team-mates have become firm friends since Smith signed from Livingston in the summer, and the new arrival believes they could be the club's first-choice strike partnership in the coming years.
"Hopefully, if we keep playing well and scoring goals and working hard," Smith said.
Laszlo has been forced to turn to the likes of Smith and Robinson as he struggles to convince majority shareholder Vladimir Romanov to sanction the loan signing of an experienced forward.
Smith admits he is benefiting from Laszlo's plight, saying: "He's not got any signings in yet so youngsters have just got to play and it's a good thing.
"There are a lot of good youngsters at the club.
"If he gets a new striker, obviously he's got to play him because he's more experienced."
Steven MacLean is Laszlo's top target but the former Rangers forward returned to Plymouth Argyle on Monday still none the wiser over his future.
Meanwhile, interest in Izale McLeod has cooled over a perceived problem with the Charlton player's knee.
Sunday's game also witnessed a debut for new Hibs goalkeeper Graeme Smith, who signed on New Year's Day after being released from his contract at Brighton.
Manager John Hughes turned to former Motherwell star Smith following injuries to Graham Stack and Yves Ma-Kalambay.
The new arrival, 26, is looking forward to a three-way fight for the jersey once his new team-mates regain fitness.
"Any club doing well, you're going to have competition," he said.
"I trained with Stacky and Maka and they're good lads - we should have a bit of fun.
"I just need to prove every day that I'm a decent goalkeeper to the manager and hopefully get a run of games."
Smith was registered just in time to play yesterday and he admitted it had been a whirlwind week.
He said: "I've had about eight hours sleep in the last four days - my daughter decided to keep me up.
"I had to drive up Wednesday night, did my medical Thursday, and then we had to wait until January 1 to tie everything up and then register.
"It's been a wee bit crazy so hopefully the next couple of days it'll calm down again and let me find my feet."
Smith chose Brighton ahead of Hibs last summer but admits he may have thought twice had he known Hughes was about to bring the likes of Anthony Stokes - who equalised on Sunday - to the club.
He added: "I remember looking at their signings when I went down the road and I was like, 'God, they're attracting big names'."