Almiron joined Newcastle from Major League Soccer side Atlanta United in January.
The Paraguay international cost a club-record fee of £21million, overtaking the £16.8m the Magpies paid for Michael Owen back in 2005.
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Almiron made his full debut in English football on Saturday, starring in the 2-0 win over Huddersfield.
Keown was seriously impressed with the 25-year-old, who once again started against Burnley on Tuesday.
And he says the last Toon player to make as much of an immediate impact was Faustino Asprilla back in 1996.
“He was breath of fresh air on his full debut,” Keown said of Almiron on BT Sport.
“The local people here are saying it’s been outstanding.
“I think Asprilla was the last player who maybe impacted as much as he did. He runs with the ball, he’s quick.
“This was virtually the first tackle on him, welcome to the Premier League, he got up after that, absolutely no problem.
“This as well, the pace of the man, and then the audacity to chip there.
“Doesn’t go in of course but the imagination that he has, the ability.
“He just went from strength to strength, running at players, he’s causing real mayhem for opposition defences.
“He tucked in that little position there, that’s where he likes to make that run.
“He takes the ball well, he looks for his team-mates, he’s not frightened of an early cross into the box.
“He’s involved in a lot of the good things that Newcastle do.
“Lots of confidence, imagination there, vision from the pass, and I think it’s really exciting for the Newcastle faithful that he’s turned up here just in the nick of time.”