Luciano Spalletti has slammed his Roma players after seeing them lose 2-1 at Atalanta on Sunday.
The 19-year-old converted a stoppage-time penalty to seal the three points for La Dea as Roma slipped up in their bid to close the gap between themselves and league leaders Juventus.
Diego Perotti had given the Yellow and Reds the lead via a 42nd-minute penalty, but the sixth-placed outfit fought back to stun their more illustrious opponents.
Atalanta continued to pour forward and won the game in the 90th minute when Ivorian teenager Kessie sent Szczesny the wrong way after Leandro Paredes had clipped Alejandro Gomez's ankle in the area. He controlled a long ball on his chest and sidefooted it to the onrushing Mohamed Salah.
Atalanta, which had picked up 19 out of a possible 21 points since September 26, attacked more in the second half and brought on midfielder Marco D'Alessandro for defender Andrea Masiello.
Atalanta also hit the post through Remo Freuler's deflected effort before Kessie's winning penalty.
Andrea Belotti scored twice in the last 10 minutes to give Torino (seventh) a 2-0 win at bottom club Crotone while Federico Bernardeschi and Josip Ilicic each netted a brace to give Fiorentina a 4-0 win at Empoli in the Tuscany derby.
It was the third time in four matches, for club and country, that the Italy worldwide netted two goals.
Lazio beat Genoa 3-1 and Bologna overcame Palermo by the same score, leaving the Sicilians one place off the bottom with six points.