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Pedro has struggled for game time this season but the Spaniard helped Chelsea prevail at Stamford Bridge, where goals from Willian and Ross Barkley saw Lampard's side into the quarter-finals.
The winger has made just 12 starts in all competitions this season, having made 52 appearances across all competitions last season.
But Lampard praised the 32-year-old and said Pedro - who made his 200th appearance for the club on Tuesday evening - could be crucial for Chelsea late in the campaign.
"I agree he was outstanding in work ethic and players look up to him for what he has done. Always a goal threat," the Chelsea head coach told a news conference.
"Parts of the season have been difficult. He was in the team at the start, got injured and then got out of the team, but what he has shown, particularly in recent weeks, is a real desire in training, to look sharp, to be giving advice and giving the place a lift with his body language.
"He can be one of our most important players until the end of the season. He is an infectious player."
Billy Gilmour, 18, also impressed for Chelsea, who had Mateo Kovacic and Willian come off with injuries.
Lampard confirmed both suffered Achilles injuries, with Kovacic's setback especially damaging for his side with another top midfielder, N'Golo Kante, already sidelined.
"Both have got an Achilles issue," he said. "Willian hopefully is not too bad, that is what he is reporting there so we will see how he is tomorrow.
"Kovacic's feels slightly worse. Hopefully not too drastic, so we'll see."