The Belgian, a United target over the summer, was instrumental in keeping Mourinho's side at bay during Tottenham's 3-0 win at Old Trafford
Why defender Toby Alderweireld should be top of Manchester United's transfer targets
As the scrutiny on Jose Mourinho's position at Manchester United intensifies following a second Premier League defeat in as many matches, the Portuguese reverted to type in his post-match comments, going on the defensive despite his side being second-best to an energetic Tottenham Hotspur.
Mourinho defended his past achievements of three Premier League titles to reporters who had the temerity to ask what he thought of his team's latest setback. It seemed to escape him these were all achieved at Chelsea, not United, where they already trail Spurs, Liverpool, Chelsea and, more surprisingly, Watford by six points after only three matches.
Defence was a running theme throughout the match at Old Trafford, mostly how abject United's composition was for the second game running and how unflustered Tottenham's back four looked during United's brief forays forward.
Phil Jones and Chris Smalling replaced the error-prone duo of Eric Bailly and Victor Lindelof following the 3-1 reversal to Brighton & Hove Albion while Ander Herrera, a trusted Mourinho foot soldier, was thrust into the starting XI too. The Spaniard was deployed as a a kind of half in, half out, midfielder-cum-defender in 3-3-3-1 formation that baffled most observers, not least MUTV, United's in-house TV channel, which initially had the returning Nemanja Matic alongside Jones and Smalling after the teamsheets were announced.
The Spaniard was exposed time and again by the forward runs of Dele Alli and Lucas Moura and was badly at fault for Spurs' second goal, playing Christian Eriksen onside while the rest of his defence stepped up, leaving the Dane free to pick out Moura for the Brazilian's first of the evening and Spurs' second goal in a little over two minutes.
Jones was at fault for Harry Kane's opener, losing flight of the ball, before injury saw him replaced midway through the second half. His replacement, Lindelof, who was dropped from the side following a poor showing at Brighton, added to the growing feeling around Old Trafford that the Swede is not up to Premier League scratch with a nervous performance that included a blind backpass to David de Gea that was almost pounced on by Alli.
Mourinho's beef with the United board in failing to add to his squad and lack of conviction in the qualities of the centre-backs already on his books are well known. And he was able to get a closer look at one player identified to address those problems on Monday.
Among the Spurs number in the 3-0 win was Toby Alderweireld, a target of Mourinho's over the summer with the Belgian centre-back looking to be on his way out after falling out of favour under Mauricio Pochettino last term.
Save for an early stray backpass that should have been punished by Romelu Lukaku and a fine save by Hugo Lloris from the Belgian striker in between Kane's opener and the first of Moura's two goals, the Spurs defence was marshaled superbly by Alderweireld, whose physical presence and ability to read and snuff out dangerous situations are qualities Mourinho's defenders lack at present.
United's defenders seem in a constant state of disarray and are the subject of constant belittling by their manager. In contrast, Alderweireld's stock is on the rise again. His performance at Old Trafford will have given both Pochettino and Mourinho food for thought.
At 29, the Belgian, who helped his country to a third-place finish at the World Cup this summer, is the perfect age for a centre-back - significant experience gained at clubs such as Ajax, Atletico Madrid and Tottenham while still to reach his peak.
Alderweireld fell from favour midway through the 2017/18 season – his position at the club compounded by demands of a significant pay rise and the arrival of Davinson Sanchez. With negotiations over a new contract - Alderweireld's current deal expires next June - at an impasse the player is free to sign a pre-contract agreement with a new club in January, which should put United - whether with Mourinho at the helm or another manager - on red alert.