* Relentless United win 25th league game of season
* Sunderland sack manager O'Neill after defeat
* Spurs bounce back to third after win at Swansea
* Chelsea slip to fourth after defeat at Southampton (Updates with Martin O'Neill departure)
By Mike Collett
LONDON, March 30 (Reuters) - Manchester United edged closer to their 20th league title when a Titus Bramble own goal gave them a 1-0 win at Sunderland on Saturday to keep them 15 points clear of Manchester City with eight Premier League games to go.
City, whose manager Roberto Mancini conceded on Thursday that their hopes of retaining the title were over, beat visiting strugglers Newcastle United 4-0 with goals from Carlos Tevez, David Silva, Vincent Kompany and Yaya Toure.
With United's match having kicked off earlier on Saturday, City took the field at the Etihad Stadium 18 points behind their rivals who set a top-flight record of 25 wins from their opening 30 matches. United have 77 points with City second on 62.
With United and City likely to take the top two spots, the race for the remaining two Champions League places hotted up with Tottenham Hotspur bouncing back from successive league defeats by winning 2-1 at Swansea City to leapfrog Chelsea into third place after their London rivals lost 2-1 at Southampton.
Spurs have 57 points, two ahead of Chelsea on 55, with Arsenal, who beat Reading 4-1 a the Emirates, on 53. Everton stayed on the coat-tails of the leading group when they beat Stoke City 1-0 at Goodison Park to move on to 51 points.
Their winner came when Kevin Mirallas set off on a mazy 70 metres run with the ball before slotting home after 28 minutes.
Arsenal's victory, with goals from Gervinho, Santi Cazorla, Olivier Giroud and a late Mike Arteta penalty, meant Reading, who had new manager Nigel Adkins in charge for the first time, dropped to the bottom below Queens Park Rangers, who also have 23 points, on goal difference. QPR visit Fulham on Monday.
Perennial relegation battlers Wigan Athletic beat Norwich City 1-0 with a late Arouna Kone goal to move out of the drop zone, at least until Aston Villa, who also have 30 points in 18th, host Liverpool on Sunday.
The decisive goal in Manchester United's win at Sunderland came after 27 minutes, when Robin van Persie ended a jinking run on the left with a shot that took a deflection off Bramble's thigh, leaving Black Cats keeper Simon Mignolet stranded.
Van Persie, without a goal in his seven previous league games - although he did score three for Netherlands in their recent World Cup qualifiers - was asked if he would claim it.
"Of course, no question about it. It's been a while so it's nice to score again and it was an important goal," the striker told Sky Sports.
It was United's seventh successive league victory and their sixth league game without conceding a goal. Their 25th win from 30 league matches was the best record in the top flight at this stage of the season since league football began in 1888.
United have now scored in their last 18 unbeaten league matches, and manager Alex Ferguson, whose side host City in their next league game, on April 8, praised his players.
"It was a battle in the second half and you have to give Sunderland credit as they had a real go at us," he told the BBC.
"We picked up two or three injuries and our goalkeeper was hurt so it was a real battling performance. We've got to win four games out of the last eight and it's important we focus on the Manchester City game, which is next at home."
Defeat for Sunderland meant they slipped one place to 16th, one point above the relegation zone, and the club reacted to their predicament later on Saturday by sacking manager Martin O'Neill.
United go to Chelsea on Monday for an FA Cup sixth round replay.
Chelsea have six matches in 16 days and began that marathon run with an indifferent performance at Southampton, where they were well beaten 2-1 by the Saints, who have already beaten visiting Liverpool and Manchester City this season.
Southampton, who climbed three places to 13th, went ahead with a Jay Rodriguez goal after 23 minutes and, although John Terry equalised with a header after 33 minutes, Rickie Lambert marked his 500th league appearance with what proved to be the winner - a 30-metre free-kick two minutes later.
Chelsea's interim manager, Rafael Benitez, told the BBC: "We have a game in hand on Tottenham. We have to carry on and be ready for the next challenge. We don't have too many options in some positions so we have to manage the squad.
"We are really disappointed. We were giving the ball away too easily. The players playing today were playing to be in the Champions League next season."
The defeat cost Chelsea ground in the race for the top four as Spurs recovered from two leageu defeats to win at Swansea with superb goals from Jan Vertonghen, his fourth in five games, and Gareth Bale, who got his 22nd this season, in the opening 21 minutes.
Bale, on the losing side for Wales in a World Cup qualifier at the Liberty Stadium four days ago, finished on the winning team this time as Spurs held out in a frantic finish after Michu headed Swansea back into the contest with 19 minutes to go.
"The team was impressive from the start," said Tottenham boss Andre Villas-Boas. "We reached the 2-0 lead very early and at halftime we spoke about getting the third goal. It didn't happen but I think the boys showed great mentality to hold on.
"It shows how ambitious they are to reach our objectives. I have to compliment everybody for their work rate defensively and offensively," he told the BBC. (Editing by Stephen Wood and Ken Ferris)