Clermont edge plucky Agen
Clermont edge plucky AgenSHARE
The result puts Franck Azema's charges in eighth place in the French topflight on 29 points after 12 matches, whilst Agen are still in the drop zone on 14.
The home side grabbed an early advantage with a try from Sebastian Vahaamahina after 46 seconds, converted by Luke McAlister.
But Agen dug in admirably as Kiwi wing George Tilsley scored three tries for the visitors with Georgian prop Vakhtangi Akhobadze adding a fourth as Jake McIntyre and Clement Laporte took two and one conversions each.
"I'm very proud of what we achieved here today because losing by a mere nine points to Clermont is enormous for us," Agen captain Antoine Miquel said.
Peceli Yato (29th minute), Benjamin Kayser (37), Remi Lamerat (47) and David Strettle (71) all added tries for Clermont, who remain unbeaten at home in the Top 14 this season.
"We were trying to get the internationals back into things and it showed in the rucks and the play," said Clermont's France veteran Morgan Parra, who made the final conversion.
"We were awful," conceded Azema.
"This is no way to prepare for a European game."
"If we play like that (against Saracens), they'll score 80 points, nothing we did was any good," he added.
Agen will rue a missed 26th-minute conversion and penalty on 32 by McIntyre and the yellow card for Ryan.
Second-bottom Agen would face a play off against the losing finalist of the second tier should they still occupy the 13th place come May.
"We'll stay up if we continue to play like that," Agen coach Mauricio Reggiardo said.
"We acquitted ourselves well here."
La Rochelle 26 Montpellier 14
Pau 27 Bordeaux-Begles 17
Brive 33 Oyonnax 30
Toulouse 31 Castres 41
Toulon 39 Lyon 11
Clermont 35 Agen 26
Stade Francais 27 Racing92 17