The United States international was in scintillating form during the first half, scoring twice and winning a penalty that Ross Barkley converted.

Pulisic's pace and composure around goal particularly stood out and Lampard was encouraged by the former Borussia Dortmund man's performance.

"I was very impressed with the way that he took the goals," Lampard said.

"As a winger in the Premier League, he has to adapt to that league.

"He is young but with huge potential and I am happy for him."

Pedro netted an audacious mid-air flick in the second half, while Michy Batshuayi scored after the break, too.

But Salzburg scored three goals of their own after half-time and caused problems throughout the contest for a shaky-looking Chelsea defence.

Lampard acknowledged his side's defensive play was a concern less than a fortnight away from Chelsea's first Premier League match of the season.

"We want to concede zero goals, so it is a concern and we want to improve on it," he added.

"We will talk about it. We can't afford to make those mistakes."

Chelsea concludes its pre-season fixtures against Borussia Monchengladbach on Sunday (AEST).