A new poll released Wednesday in the Virginia governor’s race shows that both major-party candidates are so disliked that a third-party candidate, Robert Sarvis, could be key to deciding a close election.

The poll also shows that the race has tightened, with Democrat Terry McAuliffe’s edge over Republican Ken Cuccinelli II shrinking slightly with a little more than a month to go. McAuliffe has a 3 percent lead over Cuccinelli and is receiving support from 44 percent of those surveyed compared with 41 percent for Cuccinelli, according to a new Quinnipiac University poll. That is down from a six-point McAuliffe lead.

Sarvis, who is running as a Libertarian, picked up 7 percent support.

The September survey of 1,005 likely voters found that many Virginians have made up their minds about Cuccinelli and McAuliffe, and they have decided that they do not like what they see. With only 6 percent of the respondents undecided, voters split 38 percent to 38 percent between those who have a favorable view of McAuliffe and those who have an unfavorable view. Cuccinelli’s numbers are worse; only 34 percent find him favorable, while 51 percent do not.

The poll said 85 percent of respondents have not formed an opinion of Sarvis. Peter A. Brown, assistant director of the Quinnipiac University Polling Institute, said in a statement that it is too soon to say whether Sarvis is drawing more disaffected Democrats or Republicans. Polling experts generally say surveys often overstate support for third-party or independent candidates.

“Terry McAuliffe is less disliked than state Attorney General Ken Cuccinelli. Voters are not wild about either man,” Brown said in a news rel.

The results for the major-party candidates have a margin of sampling error of plus or minus 3.1 percentage points. The poll was based on live interviews with voters on land lines and cellphones from Sept. 9 to 15.