At the time, Van Gaal's Manchester United were pleasing nobody, stodgy and struggling, but a run of six straight, ever more convincing wins sees them march to Mourinho's Chelsea fortress on Saturday with the master ready to beat his pupil for the first time.

If Van Gaal could orchestrate Chelsea's third league defeat of the season and move within five points of the leaders -- albeit having played a game more than the Londoners -- it could yet inject a smidgen of uncertainty into a race which was beginning to resemble a Chelsea procession.

Especially because Arsenal, currently seven points behind Chelsea but having a weekend off from Premier League duty to concentrate on their FA Cup defence, will then host the leaders the following Sunday.

Alternatively, it could be the start of the race's decisive week because if Chelsea win both matches, they will be effectively home and hosed, ready to savour their first title since 2010.

Van Gaal will have other ideas. The Dutchman, who gave Mourinho his big break when he was coach of Barcelona and trusted his young assistant to the extent that Mourinho would occasionally take training and give team talks, has yet to beat his protege in managerial combat.

Famously, Mourinho's Inter Milan beat Van Gaal's Bayern Munich 2-0 in the 2010 Champions League final and, when they met at Old Trafford in October, only a late, late Robin van Persie goal earned United a 1-1 draw in a game Chelsea should have won.

Now, though, United are flying and their former England full back Gary Neville, now a highly-respected TV analyst, says that, though it will be the "toughest test" yet for Van Gaal, United's performances this past month would be "absolutely outstanding in any season".

Following the most outstanding, their 4-2 derby mauling of Manchester City, the deflated champions cannot afford to feel sorry for themselves as they seek to consolidate their critical fourth place in the table with Sunday's visit of West Ham.

Southampton can leapfrog Liverpool, who have FA Cup business this weekend, and move into sixth place if they beat 10th-placed Stoke City

Meanwhile, the fascinating battle for Premier League survival sees bottom club Leicester City aim to continue their resurgence when hosting Swansea City, while Burnley, just a point ahead of Leicester, travel to 12th-placed Everton.

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