With the game still firmly in the balance at Villa Park, the No.43 on the substitutes' board was the moment when eyebrows were raised and heads were scratched in the Liverpool end.
Having seen Ollie Watkins halve a 2-0 lead early in the second half and the finely poised contest about to enter the final 10 minutes, the arrival of teenager Stefan Bajcetic was not immediately the obvious call for many as Jordan Henderson made way. After all, this was a player whose only previous experience of the Premier League was the final 20 minutes of a 9-0 win over Bournemouth in August.
Within three minutes, however, Jurgen Klopp's masterstroke had been revealed. The 18-year-old made it 3-1 with a remarkably composed finish to settle the result and ensure Liverpool returned to Premier League action after a six-week absence with a hugely important three points.
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It made Bajcetic the third youngest scorer in the Premier League era for the Reds too with only Michael Owen and Raheem Sterling ahead of him. The manager's faith and trust in him at such a vital juncture of the match underlines just how highly-rated the teen is inside the corridors of power at Anfield. Klopp reserved a trademark bear hug for the youngster at full time and it was fully deserved.
Liverpool had the lead inside five minutes through Mohamed Salah but it was a goal that owed so much to the invention and ingenuity of Trent Alexander-Arnold, who was one of six changes as Klopp welcomed back several of his big guns.
Villa probably thought they had done enough when they cleared the Reds' early corner but two touches later from the right-back - that included a sumptuous outside-of-the-boot pass to Andy Robertson - and the ball was laid on a plate for Salah to dispatch his 16th of the season.
It was Robertson's 54th Premier League assist, officially seeing him take top spot in the list of creative top-flight defenders, overtaking Leighton Baines in the process, but it was his fellow full-back who was the real architect of the move.
The debates over his curious standing in the eyes of England boss Gareth Southgate will surely never abate now, but Klopp knows exactly how best to utilise the gifted Alexander-Arnold, even if the Three Lions boss doesn't. The No.66 is the key playmaker of this team; a creative force capable of the sublime.
Darwin Nunez, as ever, was a hive of activity, scurrying and hurrying about the final third. His first-time snapshot volley from a counter-attack was well saved by Robin Olsen before he forced the Villa keeper into another stop from Alexander-Arnold's delivery. The Uruguayan was guilty of straying offside more often than not and given his blistering pace, it is something he doesn't need to do.
If he can work on timing his runs and finding the finesse at crucial times, Liverpool will have a serious threat on their hands. One run from his own half showcased that raw pace once more in the second period before he side-footed wide with his left foot.
The cries of 's*** Andy Carroll' will likely be heard at various stadia throughout the league whenever he doesn't bury the chances that are presented his way, but Liverpool know what they have in this young player with untapped potential. So too do the fans who serenaded him alongside a standing ovation when his number was called for Ben Doak late on. They even reserved an encore for Nunez at full-time when he made a beeline for the away with his fist - and his head - held high. There is a real player waiting to be unlocked in the 23-year-old and it's going to be some ride watching it all unfold.
A key feature of Liverpool's success last season was the right-sided triangle of Alexander-Arnold, Salah and Henderson, whose selfless running from wide areas allowed the other two to cause havoc from more central positions. It's something that has largely been absent this term for various reasons but it was on full display in an excellent game for all three, particularly the first half.
Villa started the second period the stronger of the two and deservedly reduced the deficit through Watkins minutes after he'd had a goal ruled out for offside. Klopp's response was to send on Naby Keita for his first Premier League minutes of the season alongside Harvey Elliott. But it was the arrival of a third midfielder that made the result safe.
It was a moment Bajcetic will never forget; his first goal in English football arrived when he rounded Olsen before squeezing past Tyrone Mings on the line. But it was a goal that again owed so much to those supplying it. This time, it was Nunez, whose rapid speed allowed him to reach Joe Gomez's ball over the top to send in the low cross for the teenager to make the most of.
That was the moment for the away end to cherish one of their heroes of yesteryear as the name Steven Gerrard echoed all around the away end. It was sung, clearly, as a playful jab towards the home crowd given the legendary Liverpool captain's stint as the Villans' manager before Unai Emery took over. It was a point that will not have been lost on those in the Holte End.
How vital this win is in the grand scheme of things won't really be known for some time, but after fourth-place Tottenham had stumbled earlier in the day at Brentford, this was the ideal way to turn the pressure up further on those above the Reds in the table. It was as hard fought as ever in this part of Birmingham, but boy it will have felt good.
With three points safely in the bag, the coveted Champions League places now just four points away and the potential arrival of £37m Cody Gakpo from PSV Eindhoven, the season could be about to be viewed in an entirely new, more flattering light.
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