They may not win the war but their comeback victory at the battle of the Etihad Stadium last weekend ensured that the Red Devils would not suffer the humiliation of conceding the championship to City, delaying the inevitable roar of triumph from their noisy neighbours for at least a couple of weeks.
United's second-half performance at Eastlands may have been as good as they have produced under Mourinho's management, as they came from two goals down to claim a dramatic fifth top-flight win in a row. That is their best run of the season, and has included three come-from-behind victories.
This form comes too late to challenge City for the title, but United have reconsolidated second place ahead of Liverpool, and will expect to open up a seven-point gap on the Reds by the end of a week in which their visit of West Brom is followed by a trip to Bournemouth.
The 71 points that United have accrued with six games to go is already the most that they have managed across a single season since the 2013 retirement of Sir Alex Ferguson, whose last game in charge was a 5-5 draw with Albion in which United striker Romelu Lukaku scored a hat-trick for the Baggies.
After receiving some stinging criticism, Paul Pogba came to the party in a big way against the Citizens with the kind of match-winning performance which made him English football's most expensive ever signing. United will be hoping this is the start of something special, rather than a flash in the pan.
Pogba's goals at the Etihad were his first since November and helped exact revenge on City following their win at Old Trafford in December. Guardiola's runaway leaders remain the only team to have beaten United on their own patch in the league all season, although Sevilla were shock victors there in the Champions League.
The bedrock to the Old Trafford fortress has been United's defensive solidity, which is little surprise considering Mourinho's managerial principles. They have kept a league-high 16 league sheets, 11 of which have been at home, and have not conceded a single goal when hosting a team currently in the bottom half of the table.
Recent Premier League form: LWWWWW
Recent form (all competitions): WWLWWW
Time will be called on Albion's eight-year tenure in the top flight should they lose to United, and Crystal Palace, Huddersfield Town and Swansea City all win.
While it seems unlikely that all three of the relegation contenders would collect maximum points, they are each at home to a club outside of the top eight.
Even if they survive this weekend, a 10-point deficit with only five games to go means that West Brom are doomed and the club is already planning for next season in the Championship with the departure of manager Alan Pardew.
Caretaker boss Darren Moore, a former Baggies defender who made over 100 appearances for the club between 2001 and 2006, stopped the rot of nine straight league defeats with the 1-1 draw at home to Swansea City.
Moore will hope to stake his claim for the permanent position by adding to the measley three league wins that Albion have managed all season, and only one of them has been away from home - at Burnley back in August.
Although either Jay Rodriguez or Salomon Rondon has notched in each of Albion's last four matches, scoring goals has been a major problem with their eight on the road across the season better than only Brighton & Hove Albion.
In total, the Baggies are winless in their last 15 Premier League away games, losing 11 and drawing four, although all of their seven away league points have come against teams that began the day in the top half of the table.
Recent form: LLLLLD
Despite Pogba's success in a more advanced role against City, Mourinho may not feel the need to include Ander Herrera in his midfield at home to the rock-bottom Baggies, which frees up an extra attacking space.
Anthony Martial and Marcus Rashford have both found starting opportunities hard to come by since the arrival of Alexis Sanchez, and it is more likely that Juan Mata is recalled to add guile to the pace of Jesse Lingard and power of Lukaku.
Defenders Phil Jones and Daley Blind remain unavailable while a former United centre-back, Jonny Evans, is a major doubt for West Brom having missed the visit of the Swans to The Hawthorns with a knee problem.
Moore opted for a 4-4-2 formation in his debut match but would be brave to replicate that at Old Trafford, which may mean a return in midfield for Grzegorz Krychowiak and a change of role for Rodriguez out wide.
Man United possible starting lineup:
De Gea; Valencia, Bailly, Smalling, Young; Matic, Pogba; Sanchez, Lingard, Mata; Lukaku
West Brom possible starting lineup:
Foster; Nyom, Dawson, Hegazi, Gibbs; McClean, Brunt, Livermore, Krychowiak, Rodriguez; Rondon
Head To Head
West Brom have won three of their nine league matches against United in the post-Ferguson era, and two of those triumphs have come at Old Trafford.
First-half goals from Lingard and Lukaku secured the Red Devils a 2-1 win in the Midlands before Christmas, and they are looking to complete their first league double over Albion since the 2011-12 campaign.
We say: Man Utd 4-0 West Brom
United are probably in the best shape they have been in since the early months of the season and could put West Brom to the sword if they get an early goal. Albion's draw against Swansea is not going to be enough to rebuild the confidence that has been shattered by such a miserable run.
In their last home fixture, also against Swansea, Mourinho's men took their foot off the gas having opened up a two-goal half-time lead, but expect them to be more ruthless this weekend as Lukaku chases 20 league goals for the campaign, and Pogba aims to silence more of his detractors.