The Celtic poster, winner of the match, Timothy Weah analyzed while the star of credit wins St Johnstone

Timothy Weah is introduced as a Celtic player in a late cameo.

Yes, he had scored goals against Airdrie and Hamilton. Yes, his ability is clear almost from the beginning.

But it was a decisive moment.

Scoring goals against smaller teams when the game is already won is one thing, but to deliver when your team really needs it is the mark of a top player.

The last 15 minutes were counted in time and Celtic was being held by an inspired Zander Clark.

After working so hard to establish his six-point lead at the Premiership summit, it would be extremely frustrating for Brendan Rodgers to see him return at the next opportunity.

And then, with time flowing and Odsonne Edward loses a wound, he turns to the 18-year-old.

The star of Paris Saint-Germain on loan had not waited for his chances on the bench. He watched, badyzed.

And four minutes after his arrival, he had a crucial impact.

Weah not only speaks with maturity beyond his adolescence, but he also plays with it.

For the opening match of James Forrest, his run from start to finish leads defender Joe Shaughnessy out of position, but the real key to the goal is his first touch.

The easiest option, which he might have been forgiven for taking since he had just started the game, would be to kill the ball and keep his back to the goal.

But he succeeds in a delicate skill that maintains his momentum and takes the defender off guard.

He can then use his pace to create a half-court that eliminates Shaughnessy from the game.

From that moment on, it's about whether or not he can deliver the ball – and if someone is there to bring the finishing touches.

Its cross-shaped center is perfectly balanced for Forrest, who rushed inside, who moved inside to occupy the space left free by the first one. Weah handle.

It is not easy to deliver either.

Weah has to adjust his stride so that his left foot is spinning around the ball and it would be easy to deflect or override the delivery.

But his three contacts were all that was needed and all three were perfect.

The goal did not leave St Johnstone open to the search for an equalizer and it would always make them vulnerable.

Scott Sinclair breaks an attack of the Saints and Weah intentionally hides near the center line.

Richard Foster is the only player on the team to come back at this point and, with the riders hammering him from every angle, he has little hope of stopping the clock.

Sinclair feeds Weah and from there, it's just about making the right decisions with a two-player advantage.

Composed, Weah chose McGregor before continuing his run into the box.

It's good to stay in the game and we can see him tell McGregor where he wants the ball.

The delivery of the midfielder is perfect and once again, Weah remains calm to place the ball under Clark and kill the match.

Weah's cameo is the perfect example of the options that Rodgers now has in attack.

There were games earlier in the season where Celtic were just as frustrated but lacked beating power from the bench.

Take the scoreless draw at St Mirren, or defeat at Easter Road.

In Weah, Celtic now has a game changer that showed he was able to perform well when his manager needed him.

Although the road ahead is still long, Sunday's showdown seemed to be one of those three points that allowed players to win long-term titles.

Not only did Celtic maintain its lead at the top, but it also exerted fierce pressure on the Rangers, who now have to get to Pittodrie and get a result.

This is a decisive week in the Premiership – and it all depends on Timothy Weah.