United manager Alex Ferguson has only lost two of 25 matches against teams managed by his former players at Old Trafford and there was little sympathy shown to under-pressure Paul Ince on Wednesday when his Blackburn Rovers side were beaten 5-3 in the League Cup quarter-final.
Ferguson also got the better of Mark Hughes, his former striker and boss of Manchester City, in a 1-0 derby triumph last weekend that put United hot on the heels of Premier League leaders Liverpool.
Keane graced Old Trafford for 12 seasons as a midfield general but even his combative qualities might not have helped Sunderland who appear to be in freefall after losing five of their last six league games.
Last week's 4-1 home defeat by Bolton Wanderers increased the pressure on him but it was still a surprise that Keane decided to leave the Stadium of Light after the first major slump in his managerial career.
United are under pressure of a different kind as they seek to build on last weekend's win at City.
They are third in the table, six points behind leaders Liverpool and five behind Chelsea, but have a game in hand on the top two and defender Rio Ferdinand said they are well placed to finish the season as champions again.
"You'd love to be leading the league from day one, but it doesn't often happen like that. We're all still confident and believe we can go on a 10 or 20-game unbeaten run," Ferdinand said on Tuesday.
"Our aim now is to make sure we're within touching distance at Christmas so we can kick on next year and reel those teams in," he told reporters.
Liverpool, who went a point clear of Chelsea at the top despite only drawing 0-0 with West Ham United on Monday, make the short trip to Blackburn, who, like Sunderland, have slid down the table after failing to win for nine league games.
Chelsea, beaten 2-1 at home by Arsenal on Sunday, visit improving Bolton, whose 4-1 win at Sunderland on Saturday was their fourth victory in five matches.
Fourth-placed Arsenal, whose youngsters were beaten 2-0 by Championship (second division) Burnley in the League Cup on Tuesday, will be back to full strength for the visit of Wigan Athletic.
Wigan will not relish playing Arsenal's first team after losing to the reserves and juniors 3-0 in an earlier round of the League Cup at the Emirates three week ago.
(Editing by Rex Gowar)
