The former Sydney Roosters player was set up on by teammate Gareth O'Brien, who minutes earlier on Saturday had missed his own glaring opportunity to clinch the winner in golden point extra time, and duly converted the goal for the first time in his career.
It earned Leigh their first Challenge Cup in 52 years, and made it a fairytale too for his dad Adrian Lam, the former State of Origin star who now coaches Leigh
"It was my first pro field goal, and it felt like I had a lot of time when I kicked it," said the Sydney-born Papua New Guinea international Lam, one of the stand-outs all season, who added the prestigious Lance Todd Trophy for his man of the match display in Leigh's 17-16 win.
"We've done a lot of work on it in the last few months because you know you're going to be in that position at some stage," added Lam.
"I dropped it a little bit on the angle but halfway towards the posts I knew it was going over. It happened really quickly. I went to celebrate and all of a sudden I was on my back."
Leigh's win, which continued an astonishing first season back among the top flight, was fashioned in the most dramatic of circumstances after Matt Parcell helped haul Rovers level with 80 seconds left of normal time.
After O'Brien missed the first chance to win it, the usually dependable Australian Brad Schneider, whose own golden point drop goal had got Hull KR past Wigan in the semi-final, came up short for Hull KR with a rash long-ranger.
It gave Lam the chance to seal a fairytale title - and the pride was etched on the face of dad Adrian, a former Wigan and Roosters star and now architect of Leigh's amazing campaign, who said: "It's just incredible to talk about how this has happened.
"This time last year we were coming in to prepare for the (1895 Cup) final. How that's gone around in the last 12 months, it's an incredible story for rugby league for us even to be here.
"I don't just want to make it about Lachlan, but it was a special moment. I've thought this week how lucky I am having him playing here for my team and doing well.
"It was just a really weird moment when he went to take the field goal, the ball was thrown back to him and I thought, he's going to win us the game here.
"I've coached him since he was six so what went through my mind was knowing how many times we'd been in the opposite position and been left heartbroken, so that was a bit of serendipity."
