Ronald Koeman said Southampton were after goals when they signed Charlie Austin as the new man scored on his Saints debut.
The team from the south coast looked the more likely team to find the net in Saturday's 1-0 win at Manchester United.
Sadio Mane, a transfer target for United last summer, fluffed a good chance when bearing down on goal in the first half and Shane Long sent a free header wide after the break.
Austin had no such trouble finding the net. Eight minutes after replacing Mane, the 26-year-old found space in the box and powered in James Ward-Prowse's free-kick.
Koeman was delighted to see his £4 million signing score the goal that earned Saints just their second win at Old Trafford since 1988.
The Southampton boss said: "I mentioned to Charlie when he came on the pitch for a free kick, go to the box and make a good header.
"That is the reason we wanted to sign Charlie Austin, a great numbers of goals."
Koeman, who has had a long-running feud with Van Gaal since they fell out at Ajax, said he expected United to put on an edgy display.
"We knew they are under pressure if you keep the organisation in your team, they will be nervous," said Koeman.
The Saints boss also used an expletive to describe reports in Netherlands that he had asked Guus Hiddink to put in a good word for him about the Chelsea job.