The Serie A trio each made it two wins from two to hold an early advantage in their respective groups.
Inter bounced back from Sunday's chastening 4-1 home loss to Cagliari, Danilo D'Ambrosio and Mauro Icardi scoring a goal in each half to see off the spirited challenge of Azerbaijani champions Qarabag 2-0 in Group F.
Qarabag now face back-to-back matches against Dnipro, who got their first point of the competition on the board via a 0-0 draw with Saint-Etienne, who are second and four points behind Inter heading into matchday three.
Fiorentina followed up their opening 3-0 triumph over Saint-Etienne's Ligue 1 counterparts Guingamp by recording the same scoreline at Dinamo Minsk - Alberto Aquilani breaking the deadlock after 33 minutes in the Group K clash before goals to Josip Ilicic and Federico Bernardeschi made the points safe.
Napoli's Slovakian playmaker Marek Hamsik celebrated a return to his homeland by scoring and teeing up substitute Gonzalo Higuain in the 2-0 triumph over Slovan Bratislava.
The competition's other unblemished records belong to Dinamo Moscow, Dynamo Kiev and Legia Warsaw.
Portuguese side Estoril are level on three points with PSV after condemning Panathinaikos to consecutive defeats, winning 2-0.
An Andriy Yarmolenko-inspired Dynamo Kiev downed Steaua Bucharest 3-1.
Aalborg bounced back from their matchday one thrashing at the hands of Steaua Bucharest, as Nicklas Helenius headed the winner in their 1-0 victory over Rio Ave.
Legia Warsaw downed Trabzonspor 1-0, gaining revenge on their Turkish opponents for two defeats in last season's Europa League group stages.
In Group L's other match, Belgium's Lokeren were also 1-0 winners over Metalist Kharkiv.
Premier League team Everton retained the lead in Group H after veteran striker Samuel Eto'o scored to help them snatch a 1-1 draw at Krasnodar.
Kevin De Bruyne smashed the goal of the night, an unstoppable long-range volley as Wolfsburg drew 1-1 at home to Lille.
Demba Ba marked his return to England with an 89th-minute penalty that cancelled out Harry Kane's well-taken opener.
Asteras Tripolis are the surprise leaders at this stage after Fernando Usero and Facundo Parra scored either side of the break to sink Partizan Belgrade 2-0.
Villarreal were comprehensive 4-0 winners over Apollon Limassol in Group A, leapfrogging the Cypriot side courtesy of braces from Gerard Moreno and Javier Espinosa.
Sevilla are top of Group G after Stephane Mbia volleyed home in injury time to earn a 2-2 draw at Rijeka.
Feyenoord chalked up a 2-1 victory over Standard Liege thanks to Elvis Manu's winner six minutes from time.
Torino and Club Brugge have four points each in Group B thanks to wins against Copenhagen 1-0 and HJK Helsinki 3-0 respectively.
