With this win, Lajong and Prayag United have seven points in their kitty, three points behind table topper Dempo FC.
Prayag drew first blood in the fourth minute of the game when Ranti Martins superbly headed a ball taken from a free kick by Vineeth CK.
Ranti struck again in the 28th minute through a spot-kick after he was brought down inside the box.
While Prayag were confident in the first 20 minutes of the game, Friday leveled the score for Lajong in the 22 minute when he headed a Sushil Kumar's cross into the net after keeper Subrata Paul was caught off-guard.
Friday struck again in the 42nd minute after L Hmar was brought down inside Prayag's penalty box to level the score for Lajong five minutes before half time.
Changing sides, Prayag changed their style of playing short ground passes as they made inroads into their opponent's defense. Lajong made a few changes too.
Boithang Hoakip who replaced 34 year-old Rennedy Singh in the 68th minute of the game scored the winning goal for Lajong when netted from a 35-yard in style.
At the post-match conference, the coaches of both teams expressed satisfaction with their boys for playing a beautiful game.
"Both sides played aggressive and put in good goals. It was a wonderful game," Lajong coach Desmond Bulpin said.
While Sanjoy Sen expressed dissatisfaction for the fact that they tasted their first lost of the season at the hands of Lajong, he said he would go home and correct what went wrong.
Lajong central defender Minchol Son (North Korea) was given the man of the match award for his dedicative effort at the back.
Lajong plays Dempo FC in their next match while Prayag plays at their home against Sikkim United FC.