Paul Morphy had an amazing ability to learn new things from his strong opponents. In his match vs Harrwitz he lost first 2 games, then he won 5. In his match vs Anderssen he lost 1st, drew 2nd and then he started winning, but Anderssen also learned from Morphy, albeit slower, and fought back later with 1 additional victory and 1 draw.
So if Morphy faced Carlsen in a match, he would lose 1-3 initial games and then turn it around. Therefore, Carlsen should win short FIDE knockout match, Morphy any other longer match.
If Morphy was time machined to this month there would be at least 2000 people who could beat him in a match.