Southampton are learning and, in many respects, fast. They are adjusting to life in the Premier League and at least appear more or less competitive in most of their fixtures, as they did at St Mary's on Sunday, when they led Fulham for almost 70 minutes and looked on course for their first league clean sheet of the campaign and a welcome three points.

They then imploded, a defence that had leaked 18 goals previously – a rate of three per game – allowing two more to sneak past them in the frantic closing exchanges. An own-goal from Jos Hooiveld did not help and it took a 90th-minute headed equaliser from José Fonte, his second goal of a low-grade encounter, to salvage a draw.

This cannot go on. Southampton might be reasonably prolific at the other end, scoring 12 times, but to rely on their lively strikeforce, especially the ebullient Rickie Lambert, to dig them repeatedly out of crater-deep holes will end only in tears and defeats.

Nigel Adkins, their manager, is acutely aware of the weaknesses at the back, which have already cost his team 11 points from winning positions this season. "We can score, that's the positive," he said. "But we're just conceding too many goals and we have to accept that.

"We've assessed it at the training ground and we're working on it. We have to defend better and as a team. But we've got four points, which is better than none considering the fixtures we've had. We allowed the game to become far too open, too stretched in the second half and really we have to be winning our home matches."

Southampton's offensive skills were more to the fore early on and they eased ahead after four minutes. Adam Lallana delivered a precise near-post corner and Fonte, the centre-back, guided in a header over Mark Schwarzer, the Fulham goalkeeper, and his helpless defenders on the line.

It was Schwarzer's 40th birthday on Saturday but, even in his youth, he would have struggled to save the looping effort, which was Fonte's first Premier League goal. Buoyed by the lead, Southampton went on to dominate, with Lambert and Jay Rodriguez constant threats in attack. Lambert side-footed wide and Jason Puncheon also went close.

At least Fulham put up more of a fight after the interval. "I was very pleased with our resilience, character and mental strength," Martin Jol, their manager, said. "In the second half we played football. In the first we were too worried about making mistakes."

Paulo Gazzaniga, the Southampton goalkeeper, had to be inspired, making two excellent saves to deny the previously anonymous Hugo Rodallega. Steve Sidwell also struck the base of a post. But the pressure paid off, albeit fortuitously, when John Arne Riise unloaded one of his left-foot specials which was clearly going wide until Hooiveld, an early substitute, stuck out a foot and diverted it in.

Kieran Richardson gave Fulham a 2-1 lead with a fine first-time shot but Fonte struck again with a header from a Daniel Fox free-kick.

Jol was unhappy that moments earlier Fulham had not been given a free-kick when Maya Yoshida fouled Richardson. "It was 100% a free-kick," Jol said. "And I thought, 'Now, we're fine, we've got the ball.' Then, two seconds later, it's a free-kick to them. If that hadn't happened, they would not have scored. But I can't say anything; I'll get into trouble. Of course I have big wages but I don't want to pay this sort of fine."

To rediscover the art of defending, Adkins would pay a fortune.

Man of the match Rickie Lambert

(Southampton)