The Welsh region were undone by first-half tries to Napolioni Nalaga, Morgan Parra and Benson Stanley and trailed 24-0 at the break - a position from which they never recovered.
"We conceded 24 points in the first half and they did not have to work for a huge amount of those points," said Easterby, who believes Clermont are good enough to reach the final after booking a home draw against Montpellier in the last eight.
"Any team where you conceded 24 points is going to be difficult, but a team like Clermont you dig a real big hole for yourself," Easterby added after his side's sixth consecutive loss in the competition.
"It's frustrating. We just fed them too much in the first half. I think it was 70 per cent possession against and 70 per cent territory.
"We just need to be far more accurate. They scored off an intercept and fed off our mistakes.
"They are a quality outfit. We gave them too much of a headstart and gave them too much they didn't have to work for."
Clermont head coach Vern Cotter was delighted with his team's performance in sealing a sixth straight pool win, with a bonus point to book a home draw in the quarter-finals.
"It was a game that was built on the first 20 minutes. I thought we were pretty serious the way we went about our work. They (Scarlets) are a team you have to get a hold of early," Cotter said.
"They are a great team. They can play good footie, as they showed in the second half. The second half was more of us defending and I was delighted we didn't concede a try.