Liverpool finally discovered how to overcome modest, if obdurate, opposition at Anfield last night. The only problem is that they appear to have unearthed the secret a little too late.

A morale-boosting victory over Sunderland moved Rafael Benítez’s team to within four points of Manchester United at the top of the Barclays Premier League and kept alive their faint hopes of ending their 19-year wait for the title.

United will reclaim a seven-point advantage if they beat Newcastle United at St James’ Park tonight and, even then, they will still have a game in hand, but at least Liverpool will travel to Old Trafford a week on Saturday with the belief that they could still make life difficult for the champions.

For 50 minutes, it seemed as though Liverpool were going to experience more frustration at home against one of the league’s less heralded teams, but then David Ngog popped up to score his first league goal for the club on his first league start at Anfield and the tension that was building around the ground eased.

In truth, it was probably more a case of Sunderland shooting themselves in the foot than anything else. The defending for Ngog’s goal was abysmal and, the moment it went in, Sunderland effectively fell to pieces, undoing all their previous good work in the process, but by the same token this was a long overdue example of Liverpool grinding out an un-pretty victory here.

Coming after a dreadful 2-0 defeat away to Middlesbrough on Saturday, it was difficult to overemphasise its importance. “The reaction of the players was very good,” Benítez said. “If United cannot win against Newcastle, it will be very good for us.”

Stoke City, Fulham, West Ham United and Hull City, among others, have left Anfield with a point this season, results that have turned Liverpool’s title bid into a torturous uphill struggle, but Sunderland failed to add their name to that undistinguished list, despite adhering to the same remit of frustrating their opponents by defending deep and getting numbers behind the ball.

The outcome might have been different had Kenwyne Jones not, in the fourth minute, spurned as glorious a chance as he will get all season.

Tal Ben-Haim picked up the ball and was granted far too much room to stroke a pass to Jones in the centre circle. Jamie Carragher committed himself, but then seemed to have second thoughts, misjudging the weight of the pass in the process and allowing Jones to jab the ball past Martin Skrtel, who had rushed to cover for his defensive partner.

With Skrtel and Carragher in his slipstream, the Trinidad & Tobago striker had only José Manuel Reina to beat but it said everything about the lack of conviction in his shot that the Liverpool goalkeeper’s save was more a formality than anything special.

After that, Sunderland retreated into their shell and began to frustrate Liverpool. But for the eagerness and endeavour of Javier Mascherano, filling in at right back after Skrtel’s horror show in the position against Middlesbrough, Liverpool rarely threatened and, at that point, another demoralising result seemed on the cards. Albert Riera had a deflected shot tipped aside, but it was not until the 51st minute that Liverpool gained the breakthrough they craved.

Riera skipped past Ben-Haim far too easily and thrust his cross to the far side, where Steven Gerrard, left criminally unchecked by Andy Reid, headed into the path of Ngog, who had the simple task of stroking the ball home. With Fernando Torres injured and Robbie Keane sold, Ngog represents about the extent of Liverpool’s attacking options, which does not say much, but he was a committed and willing performer and also had a hand in his team’s second.

Marton Fulop inexplicably spilt the France Under-21 striker’s tame overhead kick and Yossi Benayoun, the match-winner in Madrid last week, gobbled up the rebound.

“It might have been different had we gone 1-0 up early on,” Ricky Sbragia, the Sunderland manager, said. “We were pleased with the first 45 minutes and I thought we frustrated Liverpool, but we told them not to concede early in the second half and that’s what we did.”

Liverpool (4-4-2): J M Reina — J Mascherano, M Skrtel, J Carragher, E Insúa — Y Benayoun (sub: N El Zhar, 90min), S Gerrard (sub: R Babel, 82), X Alonso, A Riera — D Kuyt, D Ngog (sub: Lucas Leiva, 70). Substitutes not used: D Cavalieri, A Dossena, S Hyypia, F Aurélio. Booked: Ngog.

Sunderland (4-1-4-1): M Fulop — T Ben-Haim, A Ferdinand, D Collins, G McCartney — D Whitehead — S Malbranque (sub: C Edwards, 81), G Leadbitter (sub: D Cissé, 62), K Richardson, A Reid — K Jones (sub: D Murphy, 76). Substitutes not used: C Gordon, P Bardsley, C Davenport, D Healy. Booked: Whitehead.

Referee: M Halsey.