Sen. Mark Warner (D-VA) at a forum for candidates. (Ricky Carioti/The Washington Post)

U.S. Sen. Mark R. Warner has a 9-point lead over Republican challenger Ed Gillespie with six weeks to go before Election Day, according to a new poll that finds the incumbent’s advantage narrower than in other recent surveys.

Warner (D) leads Gillespie by 48 percent to 39 percent among likely voters, with Libertarian candidate Robert Sarvis at 6 percent, a Quinnipiac University poll found.

In a head-to-head matchup, Warner, a former governor seeking his second term in the Senate, beats Gillespie, a former White House adviser and lobbyist, by the same number of points — 50 percent to 41 percent.

“U.S. Sen. Mark Warner has been the most popular politician in Virginia for the past several years and appears to be in reasonable shape for reelection,” said Peter A. Brown, assistant director of the Quinnipiac University Poll. “But his lead is not insurmountable with six weeks to go until Election Day.”

Warner had a 22-point lead over Gillespie in a poll released about two weeks ago from the Wason Center for Public Policy at Christopher Newport University.

In the new poll, Warner has a huge lead over the other two candidates among Democrats, with 94 percent favoring the incumbent, 1 percent Gillespie and 3 percent Sarvis. And he continues to display the crossover appeal that he earned by presenting himself as a moderate, pro-business Democrat, winning the support of 15 percent of Republicans compared to 78 percent for Gillespie and 2 percent for Sarvis.

The two major-party candidates earn similar support among independent voters, with 43 percent backing Gillespie and 41 percent for Warner. Sarvis earns the support of 9 percent of independents, according to the poll.

“Sen. Warner probably has more to fear from outside rather than inside Virginia,” Brown said. “If the election turns out to be the kind of national wave for which Republicans are hoping he might be the kind of incumbent who could find himself tossed around like Republicans were in 2006 and Democrats were in 2010.”

The poll comes as Gillespie, who has been outspent 3-to-1 on television advertising, began running commercials in the expensive Washington-area media market.

Seventy-seven percent of likely voters say their mind is made up, while 21 percent say they might change their mind before Election Day.

There is a small gender gap, with women backing Warner 50 percent to 37 percent over Gillespie, with 3 percent for Sarvis. Men favor the Democrat 46 to 41 percent, with 9 percent for Sarvis.

Quinnipiac surveyed 1,010 likely voters between Sept. 17-22 for the poll, which has a margin of error of plus or minus 3.1 percentage points.