After three successive wins, Bolton Wanderers were dreaming of Premier League security, but they were yanked back to grim reality when Clint Dempsey overwhelmed their flimsy defences to leave them right back in the relegation mire.

Dempsey is coveted by bigger clubs than Fulham, and here was convincing evidence why. The USA striker scored twice in the first half to take his total for the season to 21 in 40 matches in all competitions. Fifteen of them have come in the league, breaking the club record set by Louis Saha in 2003-04. Martin Jol was clearly impressed, saying: "When you consider he has scored most of his goals operating from a wide position, his success is amazing."

Owen Coyle was named manager of the month for March after Bolton's three wins, but his team promptly regressed into defensive ineptitude and were emphatically defeated by the sort of opposition they need to be beating if they are to stay up.

Fulham were convincing winners despite the absence, injured, of Pavel Pogrebnyak, the striker who scored five goals in three games after joining on loan from Stuttgart in January.

Danny Murphy was another notable absentee, also unfit, and Jol gave a first start to Alex Kacaniklic, a 20-year-old Swede, on the left wing. Kacaniklic, who began his career with Liverpool, had impressed with a substitute's cameo against Norwich last week, but was unable to build on that, and most of Fulham's attacks were routed via Damien Duff's total mastery of Bolton's hapless left‑back, Marcos Alonso.

As is the case with the French rugby team, one tends to wonder which Fulham will turn up – the team that won three on the trot, thrashing Wolves 5-0 in the process, or their pale lookalikes who lost the next three. This time it was the real deal and they went in front at the half-hour mark when Dempsey took a free-kick from a central position, 25 yards out, and scored with a high-class strike. Adam Bogdan, reaching high to his left, got a hand to the ball but could not keep it out.

Bolton hurried and scurried in search of equality, but nobody in their starting lineup had scored more than three goals in the Premier League all season, and their shortcomings were evident whenever they came within striking range.

Fulham have no problems on that score, with Dempsey plus Pogrebnyak and Andy Johnson in reserve, and a minute into added time at the end of the first half it was 2-0 when the American, six yards out, headed home unchallenged from Duff's cross.

Leaving a player as good as Dempsey unmarked is negligent in the extreme, as Coyle ruefully admitted. "My biggest disappointment is the sort of goals we conceded. The second, on the stroke of half-time, was given away. Dempsey was allowed to run unmarked for a free header, which is hard to take," the Bolton manager said.

In extremis, Coyle went for broke, sending on Kevin Davies, Chris Eagles and Ivan Klasnic, but Fulham were always more dangerous on the break and Duff, who rounded poor Alonso at will, brought a couple of good, low saves from Bogdan.

Diarra completed the scoring after 80 minutes, sliding home John Arne Riise's centre at close range, and Bolton were booed off at the end. Facing Newcastle away on Monday promises to be tougher still. Fulham, safe from relegation, could be forgiven for taking their foot off the gas, and it is to their credit that they competed with such spirit and resolution.

Jol said: "We don't need to be looking over our shoulders at those below us, so the objective between now and the end of the season has to be to create a winning mentality and get as many points as possible.

"Playing in Europe this season has left us inconsistent afterwards, and that's something we've got to address, but this was our 49th game and to compete as well as we did is very satisfying. Bolton had won three on the trot and are fighting for their lives, but we earned the right to play our football, and if you do that and then play good football you will score goals."