Lieberman, who is running as an independent after losing the Aug. 8 Democratic primary to Lamont, leads the Greenwich businessman 52 percent to 35 percent among likely voters in the poll released Friday. Republican Alan Schlesinger trailed with 6 percent and 7 percent were undecided.
A similar poll released Sept. 28 showed Lieberman with a 10-point lead.
The debate Monday was the first time Lieberman and Lamont had faced off since the August primary. The poll showed that among those who watched the debate or read or heard about, only 3 percent said it changed their mind about their choice.
"Ned Lamont needed to score a knockout in the debates to catch Sen. Joseph Lieberman, but he apparently didn't lay a glove on him," poll director Douglas Schwartz said.
The poll suggested that Lieberman's support among Republicans and independent voters was substantial.
Lieberman leads Lamont 70 to 9 percent among likely Republican voters, with 18 percent for Schlesinger, and 58 to 36 percent among likely independent voters, while likely Democratic voters back Lamont 55 to 36 percent.
The poll also covered the race for governor, showing that Democratic candidate John DeStefano had gained on Republican Gov. M. Jodi Rell, cutting her lead from a previous poll. The poll showed Rell leading DeStefano 59 percent to 33 percent among likely voters, compared to 63 percent to 30 percent on Sept. 28.
The poll of 881 likely Connecticut voters was conducted from Oct. 17-19. It has a sampling error margin of plus or minus 3.5 percentage points.