Just before kick-off, a man with an exceedingly long beard drifted expertly away from the group of sponsors walking off the pitch and sidled up to Gabriel Jesus, Arsenal's captain for the day.
The man held up his phone and asked Jesus to pose for a selfie. Jesus looked a little bemused but he obliged anyway and the man and his beard ran off to catch up with the group, punching the air in delight.
It was the first time, but not the last, that the Premier League leaders would be made to look uncomfortable by an unexpected incursion from a team sitting 59 places below them in the football pyramid and fretting about the prospect of relegation from League One.
Arsenal survived in the end and are still on course for the Quadruple but Mansfield had beaten Sheffield United and Burnley already in the FA Cup this season and they played a quality of football in this fifth round tie way above their relatively lowly position.
Nearly 10,000 people packed into Field Mill, a home they claim is the oldest professional football ground in the world, dreaming of more glory and staring out from the Ian Greaves Stand across a modern cityscape of church spires, railway bridges and retail parks.
And they were rewarded with a thrilling match, a classic 'leveller' of a tie where a Mansfield team managed by Nigel Clough played like heroes on a mission and Arsenal clung on as the home supporters roared their hope and their encouragement.
Arsenal edged past Mansfield in the FA Cup fifth round as they beat the League One side 2-1.
But it was a tough game for the Gunners, who were pushed all the way by Nigel Clough's side.
Will Evans put Mansfield fans in dreamland when he equalised early in the second half.
Mikel Arteta made nine changes from the team that won at Brighton last week and the new boys included two 16-year-olds, Max Dowman and Marli Salmon. They both produced performances of remarkable maturity but many of the rest of the side struggled.
Maybe some will blame the pitch. This was not the kind of mudheap players had to contend with in the 1970s and before but nor was it the billiard table surface Arsenal's players are familiar with at Premier League grounds or the academies where they are nurtured.
Injuries to Leandro Trossard and Riccardo Calafiori marred the victory a little for Arsenal but fine goals from Noni Madueke and substitute Eberechi Eze - both from open play, by the way - were enough to see them through and allow them to turn their attention to their Champions League tie with Bayer Leverkusen next week.
If the task that lay ahead of them was not difficult enough anyway, Mansfield gift-wrapped a chance for Arsenal inside the first four minutes. Liam Roberts tried to pass the ball out of goal but played it straight to Dowman. Dowman advanced on goal but his shot was charged down.
After that escape, Mansfield set about doing themselves and their supporters justice. They began to dominate play and Rhys Oates dropped a shoulder and got away from Cristhian Mosquera on the left.
His driven cross was palmed away by Kepa Arrizabalaga but it fell straight to Louis Reed on the edge of the box. Glory beckoned, opening its arms wide, but even though Reed hit his shot sweetly, it was blocked by Christian Norgaard.
Arsenal began to look distinctly uncomfortable. Tyler Roberts stepped inside Salmon and sent a dipping, swerving right-foot shot agonisingly wide of Arrizabalaga's left-hand post. Arrizabalaga barely moved.
Oates was causing all manner of problems for Riccardo Calafiori on Arsenal's left flank and Mansfield peppered the Arsenal goal with shots. Arsenal faced eight attempts on goal in the first 15 minutes, the most they have to defend in that period in any game this season.
It was an open game. Roberts saved superbly at point-blank range from Gabriel Jesus and again from Gabriel Martinelli before Leandro Trossard turned a ball across goal for Dowman. Dowman was unmarked with only Roberts to beat but he took the ball first time and could only sidefoot it straight at the goalkeeper.
But Eberechi Eze’s stunner, minutes after coming on, secured the three points for Arsenal.
Arsenal did lose both Riccardo Calafiori (above) and Leandro Trossard to injury though.
It was a valiant effort from Mansfield, but the Gunners' Quadruple hopes remain alive.
Arsenal suffered a blow eight minutes before half time when Trossard went down in the middle of the pitch and had to be substituted. But two minutes after that, and against the run of play, Arsenal scored.
Roberts pushed away a low shot but Martinelli retrieved it and played it back to Noni Madueke. Madueke hit it first time, an elegant swing of his left foot, and the ball curled away from the dive of Roberts and found the top corner of the net.
Arsenal brought on Will Evans for Tyler Roberts at half-time and the second period was only just over four minutes old when Evans brought Mansfield level. Salmon, who had produced a performance of remarkable maturity, played a pass back towards Mosquera but Mosquera hesitated and Evans stole in.
Evans took Mosquera on, jinked outside him and slammed his left-foot shot low past Arrizabalaga and into the bottom corner. On the touchline, Clough punched the air in elation.
Dowman came close to re-establishing Arsenal’s lead almost immediately. He danced through the Mansfield defence in a blur of skill and quick feet and his shot was heading in until Roberts produced a fine save to push it wide.
Midway through the half, Arsenal produced the move of the game. Dowman and Madueke combined beautifully in midfield; Madueke raced away and played the ball wide to Dowman. His cross was met by Jesus, who should have scored but his prod was weak and Kyle Knoyle headed it off the line.
It was only a brief reprieve for the Stags. Arsenal worked the ball into the Mansfield area and Eberechi Eze, who had only just come on for Kai Havertz, made a yard of space for himself and crashed an unstoppable shot into the top corner. It was a moment of elite quality.
Late substitute Bukayo Saka could have added to Arsenal’s victory margin but that would have been unfair on the League One side, who had pushed the Premier League leaders to their limit.