Oleg Shatov's goal secured a second consecutive Group H win for Zenit as they overcame Gent 2-1 on Tuesday.
Shatov was on hand to finish a neat move involving the impressive Hulk midway through the second half, leaving Zenit in pole position to qualify for the last 16.
A confident start from the hosts was rewarded when Artem Dzyuba headed home just before the break, only for Thomas Matton to fire in a second-half equaliser for the hardworking visitors.
But Zenit were not to be denied and Shatov had the final say, preserving Zenit's 100 per cent start in the group.
The result leaves Gent with an uphill struggle in their bid to become the first Belgian side to reach the knockout phases, having also seen an 11-match unbeaten run in all competitions come to an end.
In contrast, the result is likely to ease criticism of Zenit boss Andre Villas-Boas, who has come under fire in recent weeks following a dismal run that has seen his side without a league win in their last four attempts.
Debutant goalkeeper Mikhail Kerzhakov was the only change made by Villas-Boas, but it was opposite number Matz Sels who was first tested, tipping Ezequiel Garay's bending 25-yard free-kick round the post after five minutes.
Axel Witsel fired over from the resulting corner, while Dzyuba placed a close-range volley wide 12 minutes later as Zenit sought an early advantage.
Gent responded and would have taken the lead in the 22nd minute had Aleksandr Anyukov not snuffed out Nana Asare's low cross at the far post to deny the onrushing Kenny Saief.
But despite enjoying plenty of possession, the visitors otherwise struggled to trouble the Zenit defence and were punished 10 minutes before the break.
A powerful run down the left allowed Hulk to expertly shake off the attentions of Rafinha inside the area, before calmly chipping an inviting ball onto the head of Dzyuba, who made no mistake with a well-placed close-range header.
However, Zenit could not build on that breakthrough and Gent, who looked reinvigorated after the break, found themselves level in the 56 minutes when Matton was on hand to lash home a teasing Sven Kums cross.
That goal galvanised the home side and a superb 67th-minute throughball from Hulk allowed Shatov to race clear into the area, before finishing with a measured chip over the despairing Sels.
Renato Neto nearly levelled again for Hein Vanhaezebrouck's men, but could only send Asare's deflected delivery just wide.
Shatov then came close to doubling his tally 12 minutes from time, after once again linking up well with Hulk, who also forced an acrobatic save from Sels late on, but a one-goal cushion proved to be enough to seal the win.
