Doubles are set for Saturday with reverse singles on Sunday to decide which team reaches the quarterfinals.
''I played really well,'' Fognini said. ''Monaco never give in, but playing at the top was the key for me.''
Argentina is playing without its top player Juan Martin del Potro, who has chosen to skip Davis Cup and focus on tour events.
Berlocq gave Argentina a perfect start.
''I felt like you have to feel in a Davis Cup match - with determination and dedication,'' Berlocq said. ''When I was on the court and fans screamed 'gladiator,' it gave me a lift.''
Argentina is a four-time runner-up in the Davis Cup but has yet to win tennis' top team event. Italy has won once.
The winner faces either Britain or the United States in the quarterfinals.
- Sports & Recreation
- Fabio Fognini
- Carlos Berlocq
- Juan Monaco
- Davis Cup