Striker Chris Wood took his Lions tally to five goals since arriving on loan in September with a brace either side of the break, while James Henry and Liam Trotter added goals after 78 and 87 minutes respectively.
"The result pleases me a lot. It was a tight game for quite a long time and I couldn't necessarily see the 4-0 coming," said Jackett.
"The second goal was a very good goal from our point of view after we'd been under a bit of pressure and I think that's what killed the game off. I couldn't see us losing once we'd got that second.
"I thought Darius Henderson was terrific up front. He hasn't got on the scoresheet himself but his link-up play with Chris Wood was really good.
"Chris is a goalscorer and he has produced two very good finishes today but I think even he will say that he has got the perfect foil in Darius.
"We have got Chris on loan from West Brom but there has been no dialogue between the two clubs as yet about that going any further.
"I've read in the press that Chris has said he's pleased to be here and that's nice for me to read.
"He's been on loan at one or two clubs before but maybe not played as much as he has done here. We're glad to have him."