Toulouse claimed a 42-27 bonus-point victory over Wasps, while there were also European Champions Cup wins for Glasgow, Saracens, Leinster and Castres on Saturday.
Toulouse, who had Cheslin Kolbe on the left wing and Rynhardt Elstadt at openside flank, scored five tries at Stade Ernest-Wallon, including two from scrumhalf Antoine Dupont.
Wasps trailed just 22-20 at half-time, thanks in part to a try from fullback Willie le Roux, but that was as good as it got for the visitors.
Toulouse’s fourth win in as many matches puts them top of Pool 1, two log points ahead of Leinster, while Wasps remain rooted to the bottom after losing three and drawing one of their four games.
Toulouse and Leinster, who scored six tries in their 42-15 win against Bath, will meet in round five in a pool decider.
In other results on Saturday, the Glasgow Warriors kept their quarter-final hopes alive after a 21-10 win over Lyon at Scotstoun Stadium, and Saracens cemented top spot in Pool 3 with a 26-14 win over the Cardiff Blues at the Arms Park.
Castres blew Pool 2 open after a dramatic 13-12 victory over Munster at Stade Pierre Fabre. With two rounds remaining, Munster top the pool on 12 points, followed by Castres (nine), Exeter and Gloucester (both on eight). On Friday night, Exeter put a massive dent in Gloucester’s playoff hopes with a 29-17 bonus-point win at Kingsholm Stadium.
In Friday’s other match, Ulster kept the pressure on Racing 92 in Pool 4 with a 30-15 bonus-point win over the Scarlets at the Kingspan Stadium.
Round 4 results:
Ulster 30 Scarlets 15
Gloucester 17 Exeter 29
Glasgow 21 Lyon 10
Cardiff Blues 14 Saracens 26
Toulouse 42 Wasps 27
Leinster 42 Bath 15
Castres 13 Munster 12
Leicester vs Racing 92
Newcastle vs Edinburgh
Montpellier vs Toulon