An increasingly agitated Hafiz Haciyev of the Modern Musavat Party pounded the table repeatedly and gestured threateningly at his opposition rival after Hasanli accused the administration of incumbent President Ilham Aliyev of rampant corruption.
"I will destroy you," Haciyev shouted at Hasanli at one point.
As the exchange continued and Hasanli challenged Haciyev and other candidates to account for billions in missing funds, Haciyev stood and threw the plastic bottle at Hasanli, who was seated across the table.
The object ricocheted off the table in front of Hasanli without striking him.
Haciyev was quickly escorted from the studio with the assistance of security guards.
Hasanli is generally regarded as the only viable opposition voice in the race, facing two-term incumbent Aliyev and a field of mostly pro-government candidates ahead of the October 9 election.
He used much of his time in the September 19 debate, the second of what are slated to be twice-weekly events, to rail against corruption and accuse Aliyev and his family of wrongdoing.
After the kerfuffle, Hasanli continued an animated argument with the moderator over whether he should be granted extra time to make up for the interruption, which came during his six minutes of alotted time.
Six minutes later, an exasperated Hasanli stood up and left the studio.
By then, two other candidates who had finished their own statements were also gone, leaving six of the original 10 people onstage with the moderator.
Aliyev, who is running for a third term, sent a representative to the debate to read from a prepared statement.
Hasanli emerged as the opposition choice after the authorities nixed the notion that Moscow-based filmmaker and National Council of Democratic Force Chairman Rustam Ibragimbekov, a dual Russian-Azerbaijani citizen, would meet the criteria for registration.