Grimsby, after carving out chances in the first half, fell behind to the Wearsiders five minutes into the second when Kevin Phillips finished from Nicky Summerbee's inch- perfect pass. And although the Mariners worked hard, Sunderland had the cutting edge and Lee Clark added a second goal to keep them 12 points ahead of the chasing pack.
Meanwhile, lowly Crewe, inactive since winning at Bolton, had clearly put the lay-off to good use and won away again, 2-1 at Swindon Town. First- half goals by Rodney Jack and Phil Charnock put them on track and although Chris Hay's second-half strike threatened to derail the Railwaymen, Alex held on.
None of the sides jousting for the second automatic place to the Premiership blinked as Ipswich Town, Bradford City and Bolton Wanderers all won.
Second-placed Ipswich Town, beaten at lowly Crystal Palace in mid-week, recovered with a 3-0 win over Huddersfield Town. Jim Magilton, in the last game of his two-month loan spell from Sheffield Wednesday, got them off the mark in the 13th minute with a right-foot shot and David Johnson's 15th goal of the season on the stroke of half-time made the second half more comfortable. Bobby Petta added the third.
Their East Anglian neighbours, Norwich City, were thrashed 4-1 at third- placed Bradford City, who were 4-0 up at half time. Peter Beagrie, who tucked away a 25th-minute penalty to put Bradford 2-0 up, orchestrated their best moves, Lee Mills scored to take his season's total to 21, and Jamie Lawrence scored the pick of the goals, dashing 30 yards through the porous Norwich defence to slip the ball past Andy Marshall. Perhaps the Norwich director, Delia Smith, should look at the Canaries' pre-match menu.
In the second half they pulled a goal back and Bradford had John Dreyer sent off, but the game had been won and lost long ago.
Bolton, who had gone five games without a win and conceded three goals in each of their three previous matches, got back into winning ways with a 2-1 victory over Queen's Park Rangers at the Reebok Stadium, Bob Taylor scoring both their goals.
In the ruck tussling for the fourth play-off place, Wolverhampton Wanderers made the biggest gain, jumping from ninth to sixth after defeating struggling Bristol City. Haarvard Flo scored twice in the 3-0 win. Sheffield United kept pace after a fright at Tranmere Rovers. Trailing 2-0 at half-time, Traianos Dellas scored two in their eventual 3-2 win.
The Second Division play-off hopefuls Manchester City, Gillingham, and Bourne-mouth, beaten at home for the first time in a year, all lost while in the Third, the leaders Cambridge United lost and second-placed Cardiff City drew. It's a very nervy time of year.