Results elsewhere meant United would have gone down regardless of the result at Old Trafford. But Law was distraught. He was immediately substituted and did not kick a ball again in league football.
Manchester City 5-1 Manchester United, Division One, September 1989
Alex Ferguson was entering his third full season as United manager and having seen his side finish the previous campaign in 11th place, he looked no closer to ending their 22-year wait for the title.
The 1989-90 season's first derby at Maine Road was to prove a personal horror show for the Scot as David Oldfield inspired promoted City to their biggest derby win since 1955.
But United ended the season as FA Cup winners, buying Ferguson valuable time, and it would be 13 years before they next tasted defeat in the derby.
Manchester United 5-0 Manchester City, Premier League, November 1994
Having ended their long wait for the English title in 1993, United followed it up with a league and FA Cup double in 1994. The derby at Old Trafford later that year reflected the gulf that had opened up between the two Manchester teams.
Russia winger Andrei Kanchelskis scored a hat-trick and there were also goals for Eric Cantona and future City manager Mark Hughes as United returned to winning ways after a humiliating 4-0 defeat by Barcelona in the Champions League.
Manchester United 1-6 Manchester City, Premier League, December 2011
Ferguson dismissed City as the "noisy neighbours" following their acquisition by the mega-rich Abu Dhabi United Group in August 2008. But he could no longer dismiss the racket being made across town following this galling reverse at Old Trafford.
Mario Balotelli's brace put City in control, the controversy-prone Italian famously revealing a T-shirt that read 'Why Always Me?' after opening the scoring. But it was Jonny Evans's dismissal early in the second half that proved decisive. Sergio Aguero, David Silva and Edin Dzeko, who scored twice, hammered home the visitors' numerical advantage.
It was United's heaviest home defeat in 66 years and Ferguson called it his "worst ever day".
Five months later, City pipped United to the title — their first since 1968 — on goal difference after Aguero's injury-time strike secured a heart-stopping 3-2 home win over Queens Park Rangers on the season's final day.