ONE minute they were asking one another who he was, the next they were singing his name.

Celtic supporters have no way of knowing what Tony Watt will amount to as his career unfolds, but those who saw his debut at Fir Park will not forget it in a hurry. A drab match was goalless and going nowhere until the 18-year-old came off the bench after almost an hour. Teenagers rush into most things in life. Watt did not waste time in scoring a goal, then another.

It was sunny in Lanarkshire but nothing shone more brightly than Celtic's single Watt bulb. He cost £100,000 from Airdrie United 15 months ago but did not get a first-team look-in until yesterday. Neil Lennon had picked a team for the benefit of one little-seen striker, Pawel Brozek, only for Watt to hijack his day.

The young lad hijacked Motherwell's too. Some of the home fans had a banner alluding to their possible entry to next season's Champions League. Third will be good enough to earn a place in the qualifiers because of Rangers' ineligibility. That should be a big deal to Motherwell supporters but it doesn't seem to have mobilised them en masse, given that fewer than 4000 home fans turned out. That was a poor response for a team which has served them well this season but could yet end up with only a Europa League place. They are only three points ahead of fourth-placed Dundee United, who have momentum. Those clubs meet at Fir Park on the final day of the season. Motherwell's most obvious failing in the Clydesdale Bank Premier League has been to take nothing from either of the Old Firm all season and they never looked confident about inflicting harm on a Celtic team which had lost three of its previous five matches.

Lennon was in an experimental mood. From his seat in the stand, where he served the first of his two-game suspension, he watched as Charlie Mulgrew, Thomas Rogne and Victor Wanyama operated as his three-man central defence between a pair of wing-backs, Emilio Izaguirre and Cha Du-Ri. Joe Ledley and Ki Sung-Yueng sat behind Kris Commons, who worked the space behind strikers Gary Hooper and Brozek. The Pole joined Celtic in January with a view to getting a run of appearances and goals to play him into contention for his country's Euro 2012 squad.

Instead he has been on the margins, and it showed in the rustiness of his play. After just over half an hour he missed the best chance of the first half after Wanyama slipped through a pass to play him in. His poked finish was poor and wide. Another chance came just before half-time. His low, angled shot squirted through Darren Randolph's legs and the goalkeeper was fortunate to see it run across his goal and out of play just before Hooper – Celtic captain for the day – arrived to stroke it into the net. That was effectively the last seen of Brozek, who petered out before being replaced by Watt.

Commons, who looks like he might be coming into some bright form as the season ends, offered more.

Until the goals there was a sense that Celtic were there for the taking, less in need of any points than their hosts. There was no great urgency in their play. But Motherwell's control and passing often let them down, even if they did occasionally get behind Lennon's unfamiliar back line.

Chris Humphrey's pace was an issue for Celtic and it was his volley across goal which forced Lukasz Zaluska into a lively save. Steve Jennings tried his luck with a long-range lob. Ki appeared to pull a muscle just before half-time and the away supporters, and maybe some in the home ranks were glad to see Paddy McCourt brought on. The match needed an injection of the sort of creativity McCourt can provide. No one suspected it would be another of the substitutes who would rewrite it all.

Watt's introduction had seemed inconsequential, a footnote in a match at the fag end of Celtic's season. He had been playing for only four minutes when Wanyama got in behind the Motherwell defence to fire a ball across the goal. Watt met it at the back post, lashing it so forcibly it almost carried Randolph into the net. Another couple of minutes, another goal, this time taking Ledley's pass and controlling it before burying a shot through a defender's legs into the corner. They were the goals of an instinctive finisher. Watt, looking lively and physically strong, was the archetypal impact substitute. McCourt planted a cross into the goalmouth and on to Cha's head for the late third.

Only one Celtic man might have been in two minds about their new headline-making striker. No-one would have blamed Brozek for watching it through the cracks in his fingers.