Some Swansea fans turned up late, bemused by the 7.05 kick-off. They were not alone: the opposition did not start playing until 7.30, by which time they were three goals in arrears and this Europa League qualifying tie was effectively over before the away leg next Thursday. Petrolul's coach, Cosmin Contra, gave his team a 5% chance of now going through, but he is renowned for erring on the optimistic side.

Swansea are away to Tottenham on Sunday and this was a case of anything you can do, we can do too. Spurs had scored five against Dinamo Tbilisi earlier in the evening and Michael Laudrup's slick passing team gave the north London thoroughbreds no psychological advantage in that respect. "Now let's hope for 5-5 on Sunday", Laudrup said, smiling.

The Romanians were without their regular right-back, who was suspended, and Wayne Routledge gave the understudy, Sebastian Achim, a chasing he will never forget, running past the young defender at will and scoring twice before he was substituted, with the trip to White Hart Lane in mind. For the same reason Laudrup brought off Jonjo Shelvey, who was outstanding in midfield.

The Swansea manager is a believer in squad rotation – "I don't have a best 11", he said – and made three changes. Nathan Dyer was unavailable with hamstring trouble and gave way to Pablo Hernández. Also out were Ben Davies and José Cañas, whose places went to Neil Taylor and Wilfried Bony. The promotion of Bony from the bench to operate as principal striker enabled Michu to revert to the role he favours, just behind the main man. This in turn allowed Shelvey to drop back into a deeper midfield position, replacing Cañas. The resulting deployment had a lovely balance, their crisp passing and cohesive movement much too good for the low grade visitors.

Ploiesti are hardly a big draw and the crowd was 8,000 short of a full house. For those without an anorak's interest in east European football, they finished third in the Romanian League last season, a distant 17 points behind the champions, Steaua Bucharest. They qualified for the Europa marathon by winning the Romanian Cup final, in which they beat Cluj 1-0.

Dominant from the outset, Swansea were ahead in the 14th minute when Routledge's shot was deflected in by Ovidiu Hoban, and from then on there was never the slightest doubt about the outcome. The second goal came in the 22nd minute, with Routledge again its instigator. This time the winger slipped a short pass through to Shelvey, whose left-wing cross reached the far post, where Hernández's contact set up Michu for an emphatic finish.

Three minutes later Hernández, out on the right, found Routledge unattended at the far post, where he dispatched his second with a header from three yards. He might have had his hat-trick before half-time, but after impressive interplay between Shelvey and Michu his drive from the 18-yard line was inches over.

By the interval the only question left to be answered was how many goals Swansea would rattle in, and a minute into the second half Bony turned smartly six yards out and shot powerfully against the crossbar.

The striker from the Ivory Coast, a £12m buy from Vitesse Arnhem, did not have to wait much longer for his fourth goal in as many appearances for his new club. It was a scruffy affair, Bony bundling the ball under the goalkeeper at the second attempt, but talk of an own-goal by the keeper was refuted by all concerned.

His job well done, Routledge was now withdrawn and his replacement, Alejandro Pozuelo, lifted the ball expertly over the advancing goalkeeper from six yards for number five. Oddly, however, the goal of the night came from the Romanians, after 87 minutes, when Gheorghe Grozav beat Michel Vorm to his left with a spectacular overhead kick from near the penalty spot.

England need the penetrative width Routledge supplied here, but Laudrup was not being drawn into that. "I'll leave it to Roy Hodgson, he said. "But if you play as well as Wayne is doing, you always have a chance."Laudrup said: "We played very well, kept the ball and gave nothing away. I'm very pleased we'll be going through to the group stage." Realising he could be accused of counting his chickens, he added: "They need a miracle, but miracles happen for a reason. If we go there and we are strong and competitive again, we will go through."