Despite their manager’s strong record, Wales knew this was going to be their biggest test of the WCQ cycle, but even the most pessimistic amongst them couldn’t have envisaged such a nightmarish opening half-hour.
It was simply men against boys, as the yellow-clad Red Devils tormented their visitors from the off and took the lead via a 15th-minute penalty, which came from a Brennan Johnson handball at the end of a Kevin De Bruyne shot.
The VAR review that followed was a lengthy one, but once the green light was given, allowing Romelu Lukaku to calmly roll the ball into the bottom-left corner past a wrong-footed Karl Darlow.
Lukaku scarcely had time to enjoy any limelight from his 89th international goal, as Belgium doubled their lead four minutes later.
De Bruyne again played a role, as he advanced with intent on the Welsh backline, before feeding Maxim De Cuyper, who in turn squared the ball for Tielemans to sidefoot into the net.
Wales might then have halved the deficit, as Ben Davies saw Matz Sels parry away a long-range effort.
But normal service immediately resumed, and not long after Jérémy Doku almost got an assist – after De Bruyne missed the target by inches from his perfect through-ball – he marauded into the box and found the bottom-left corner with a blistering shot that Darlow could only get fingertips to.
Belgium eased off slightly – but perhaps too much, as Wales were given something of a lifeline just before half time.
Sels felled Chris Mepham in an aerial duel at the end of a corner, and from the subsequent penalty, Harry Wilson drove the ball into the opposite corner.
That somewhat changed the complexion of both managers’ half-time team talks, and Belgium again came out the stronger.
Dodi Lukebakio should have choked out any chance of a comeback just a minute after the restart, when he received a deft ball from De Bruyne and found himself one-on-one with Darlow, only to fire wildly over the bar when a goal looked inevitable.
That looked all the more costly on 51’, when Wales reduced the deficit to one. Johnson and Wilson exchanged passes as they broke down the right flank, and with a pinpoint ball across the deck, the latter found an onrushing and unmarked Sorba Thomas, who lashed the ball low into the far corner.
Despite their newly precarious situation, Belgium then found extra reserves of energy, and Davies was on hand to deny Lukebakio with a headed block, as he tried to shoot on the end of another well-worked De Bruyne ball into the area.
Wales looked to have been stifled, but after a double switch that brought fresh ideas to the attack, the incredible happened with just over 20 minutes remaining, as Wilson found Thomas just past the far post.
The Nantes loanee spotted Johnson in space dead centre of goal, and with a headed pass, he found the UEFA Europa League final hero in virtually the same spot he conceded the earlier penalty, with the man himself heading powerfully into the net to complete Wales’ improbable fightback.
It was anyone’s game from there, and after seeing a Lukaku goal disallowed, De Bruyne got on the end of a Tielemans cross to net Belgium’s winner at close range.
It was a big blow for Wales, but they showed more than enough to suggest that a second successive FIFA World Cup appearance is within their capabilities.
As for Belgium, they have now won 12 of their last 15 WCQ home games, but will hope for stronger showings from here to make good on their status as Group J favourites.
Flashscore Man of the Match: Harry Wilson (Wales)