At the beginning of the year I thought this would be never a question, between these two teenagers Fonseca was rated much higher and he had also came out stronger from the nextgen finals last year.
But now surprisingly they are having a pretty comparable season:
Fonseca has won more title (ATP250 Buenos Aires), has better overall W/L ratio. He also got past the first round in all 4 slams and won 6 slam matches in total (Tien won 4 matches). Fonseca also won their encounter this year.
Meanwhile, Tien has achieved higher ranking (#36 vs #43) and deeper runs in bigger tournaments (R4 at AO, R4 Canadian masters + an ATP 500 final). Both his slam R1 exits are by high-profile players (Zverev at FO, Djokovic at USO), so there's a bit bad luck compared with Fonseca.
Note that Tien got 5 top-10 wins this year, only behind Alcaraz and Sinner, compared with Fonseca's only 1 top-10 win against Rublev (though admittedly most of his opponents did not play top-10 worthy tennis). On the other hand, Fonseca seems to be more consistent at beating average ranked players.
Tien's good results concentrated on hard courts, and he has done very little outside that. Fonseca was more even across different surfaces.
Overall it's quite close, but for me, Tien is having a better season by a margin, unless Fonseca could do something special in the indoor season.
But now surprisingly they are having a pretty comparable season:
Fonseca has won more title (ATP250 Buenos Aires), has better overall W/L ratio. He also got past the first round in all 4 slams and won 6 slam matches in total (Tien won 4 matches). Fonseca also won their encounter this year.
Meanwhile, Tien has achieved higher ranking (#36 vs #43) and deeper runs in bigger tournaments (R4 at AO, R4 Canadian masters + an ATP 500 final). Both his slam R1 exits are by high-profile players (Zverev at FO, Djokovic at USO), so there's a bit bad luck compared with Fonseca.
Note that Tien got 5 top-10 wins this year, only behind Alcaraz and Sinner, compared with Fonseca's only 1 top-10 win against Rublev (though admittedly most of his opponents did not play top-10 worthy tennis). On the other hand, Fonseca seems to be more consistent at beating average ranked players.
Tien's good results concentrated on hard courts, and he has done very little outside that. Fonseca was more even across different surfaces.
Overall it's quite close, but for me, Tien is having a better season by a margin, unless Fonseca could do something special in the indoor season.
