The Slovakia international netted twice in the 4-1 first leg victory as Rafael Benitez's side took a huge step towards sealing a semi-final berth.
After a cagey opening 10 minutes Napoli settled into their rhythm and executed their plans to devastating effect – with Gonzalo Higuain and Manolo Gabbiadini also on the scoresheet.
"It was a great performance we didn't expect this result, even if we could've done even better," he told Mediaset.
"It's a shame we conceded that goal late on, but the important thing is that we got four away from home.
"It's not over yet, but we have made a huge step towards qualification for the next round."
Napoli travel to Cagliari in Serie A on Sunday looking for a third successive win in all competitions, before welcoming Wolfsburg to San Paolo on Thursday.
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