A question-and-answer session during which the candidates could ask each other questions offered perhaps the most revealing view into where each felt their opponent was most vulnerable.
Gomez asked Markey to name a time when he had opposed a tax supported by his party — a line of attack Republicans have pushed previously — and Markey faltered, saying only that he had voted to reduce taxes on the middle class during his time in Congress by $1 trillion and had fought tax breaks for big businesses.
Markey asked Gomez to name a circumstance when a citizen would need to use an assault weapon on the street, aiming to snag him on his objection to an assault weapons ban. Gomez, too, dodged the question, instead touted his proclaimed independence and support for the Toomey-Manchin bill that would expand background checks.
"We both know that only one of us here can go down to D.C. and actually get this bill passed when we go down there, because it's going to take bipartisan work to get Republicans on board and to get the conservative Democrats on board," he said.
Gomez also charged that Markey had been "craven" to use the Newtown, Conn., massacre in an ad hammering Gomez on his gun control views.
A particularly combative exchange came over term limits, when Markey charged Gomez was hypocritical for criticizing him for his time in office due to the support he's received from Sen. John McCain (R-Ariz.)
Gomez, who has proposed a two-term limit for senators, claimed he had told McCain he should be term-limited during his campaign stop in Boston last month, but Markey pushed back on the claim.
"Mr. Gomez did not tell John McCain that this is his last term," Markey said. "That did not happen."
The two sparred back and forth for minutes over whether Gomez had or had not spoken to McCain about his long tenure in Congress.
And the two hammered each other on lines of attack that they've leaned on consistently throughout the campaign: Gomez's refusal to release details on his private equity career; and Markey's residency.
Markey questioned why Gomez hadn't released his client list, asserting that the names of his clients are "important," while Gomez charged that Markey had an incomplete understanding of private equity.
“If you knew what private equity was, you’d know that we don’t have clients,” he said.
He also noted that President Obama invested in his firm at one point.
And Gomez questioned why Markey's address had been redacted from his tax returns. The congressman's residency has been an issue throughout the campaign, as he calls Malden, Mass., his hometown and keeps a house there, but spends much of his time in Maryland.
Markey said the redaction was an accountant's error.
Gomez's campaign released an internal poll hours before the debate that showed him down by just seven points, a position that puts him "in striking distance of pulling off a victory," according to a memo from Gomez's pollster.
Former Sen. Scott Brown (R-Mass.) pulled off a last-minute upset in 2010, and Republicans are hopeful Gomez could surge in the final days of the campaign.
But the most recent independent poll gave Markey a 13-percentage-point lead over Gomez, and Markey maintains a substantial advantage in fundraising and on air.
Voters will head to the polls on June 25 to elect a replacement for Secretary of State John Kerry (D).