Wing Teddy Thomas touched down twice for Biarritz in the first period, with hooker Arnaud Heguy also crossing prior to the interval before centre Benoit Baby and replacement back rower Seremaia Burotu handed the visitors a 41-17 lead with five minutes remaining.
Gloucester, who opened the try scoring through Mike Tindall just before the game was a quarter of an hour old, added two more tries at the death, but Lund would have been happy to hear that Biarritz were good value for their place in the last four as they produced a power-packed performance up front and a devastating display out wide.
"I can't really remember any of the tries but the boys told me afterwards that the maul worked well and we scored a couple of times off the back of that," Lund told this website.
"That's something that comes with confidence. We've got the confidence to maul that way now.
"If it doesn't come straight away, we don't worry, we don't rush it. We just let it build and try and stick together.
"That's the main thing, because it doesn't have to move quickly. It can go slowly for five metres and then speed up. That was definitely a big confidence booster for our team."
Thomas' second try just past the half hour and Heguy's effort three minutes before the interval were direct results of fearsome forward drives, while Thomas' first and Baby's 57th minute score were brought about by brilliant breaks from wing Takudzwa Ngwenya.
The United States international cut loose from inside his own half to set Thomas on his way after 22 minutes before sprinting outside a broken defensive line on his own 22 to hand Baby his simple run in, much to the delight of Lund and his colleagues up front.
"The backs also used the ball a bit and we played out wide," added the former Leeds player.
"We've had terrible weather in Biarrritz. It's not been cold but there's been a lot of rain and the pitch has been quite heavy. We know we've got guys that can play like that but it's not been a possibility.
"We showed here that, if we can keep the ball and send it out wide, we've got guys with a lot of pace. Benoit Baby has completely changed his game in the last two or three months. He's really come on and he's probably the best player in our team at the moment, he's playing that well.
"When they're firing, it's great for us forwards - you just run behind them to be honest!"