"It was the first time, quite honestly, that I've been a bit afraid of making a mistake," Totti, who has made a club record 759 appearances for Roma, told Sky Sports when asked about the penalty. "I couldn't afford to miss under the South Curve, in front of my fans."
Sudden and heavy rain meant the start of the second half in Rome's Olympic Stadium was delayed for more than an hour because of a waterlogged pitch.
The weather also hit Genoa's home match against Fiorentina which was abandoned after 28 minutes, with the score at 0-0, because of a fierce hailstorm.
England goalkeeper Joe Hart had a debut to forget at Torino, where he moved on loan 12 days ago after losing his first-team place at Manchester City.
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Torino lost 2-1 at Atalanta after Hart misjudged a corner cross in the 56th minute, leaving space for Andrea Masiello to equalise for the home side.
When Atalanta were awarded a penalty in the 82nd minute, Hart dived the wrong way as Franck Kessie scored the Bergamo side's second goal.
Mauro Icardi's stoppage-time strike earned Frank de Boer his first win as Inter Milan coach, a 2-1 defeat of promoted Pescara. Argentine Icardi had also scored the opener, in the 77th minute, and has now notched up 50 goals for Inter.
AC Milan defender Luca Antonelli was taken to hospital with a suspected head injury after colliding with a team mate in his side's 1-0 defeat to Udinese at the San Siro.
The Milan club gave no immediate details of the Italy international's condition.
(Writing by Clare Fallon; Editing by Martyn Herman)
