Leeds Carnegie collected their first win of the season in a tight Pool 4 encounter away to Bucuresti Oaks.
19-year-old Christian Lewis-Pratt inspired the English side to victory at a rain-sodden Stadionul Arcul de Triumf.
It was the third time in the last 12 months the two sides had met having been drawn in the pool stages of last year's tournament.
Henry Fa'afili scored an injury-time try for the visitors to add to an earlier penalty try while the hosts could only manage three Florin Vlaicu penalties.
Cavalieri Estra 23-21 Connacht Rugby
Cavalieri Estra picked up the first Italian win on the opening weekend of European action as they famously downed last season's semi-finalists Connacht 23-21 in a thrilling game.
A long range try from South African-born lock Wouter Moore eventually proved the difference between the two sides, although Connacht outside half Ian Keatley hit the post with a last gasp drop goal to regain the lead for the Irish side.
The home side were 10 points adrift at the interval, but hit back to dominate the second period and get off to a great start in Pool 4.
Exeter Chief 13-20 Montpellier
Montpellier continued their good start to the season with victory over Exeter at Sandy Park.
An early Dimitri Pelo converted-try put the visitors in the driving seat in Exeter's first European encounter.
Montpellier fly-half Raphael Lagarde kept the scoreboard ticking over to give them a 13-6 halftime lead, the Chiefs only points coming from the boot of Ryan Davis.
But Seta Tuilevuka struck with a devastating try shortly after the interval to blow the hosts away.
But the Chiefs came back and scored a try of their own thanks to Chad Slade in the final minutes. Davis kept his cool and converted to snatch an unlikely losing bonus-point
Elsewhere La Rochelle recorded a 38-3 victory over Rovigo in Italy, the visitors picking up a bonus point along the way scoring six tries in this Pool 5 game.