[cnn-photo-caption image= http://i2.cdn.turner.com/cnn/2009/images/10/30/art.bloomberg1030.gi.jpg caption="NYC Mayor Bloomberg up by double digits in home stretch."]
(CNN) - A new survey suggests that New York City Mayor Michael Bloomberg, vying for a third term in office, holds a 15-point lead over his Democratic rival, with just four days to go before voters there head to the polls.
According to a Marist College survey released Friday, 53 percent of likely New York City voters support Bloomberg, running as an independent, with 38 percent backing the Democratic candidate, New York City Comptroller William Thompson. Nine percent of those questioned are undecided, or backing other candidates.
Bloomberg held a 16-point advantage in a Marist poll conducted last week and was up 18 points over Thompson in a Quinnpiac University survey released earlier this week.
Bloomberg holds an even bigger lead over his rival in another key campaign measure: he's spend more than $33 million on TV ads, according to an analysis of New York City's mayoral race by TNSMI-CMAG, CNN's consultant on campaign ad spending. Bloomberg's launched 50 different ads during his re-election bid, which have aired more than 11,000 times. Bill Thompson, Bloomberg's Democratic rival, has spent just over $2.66 million on TV ads.
The Republican-turned-independent mayor has outspent most of the Republicans who ran in last year's presidential primaries, according to TNSMI-CMAG's Evan Tracey - his $33 million outlay is more than three times what John McCain spent to win the GOP nomination, and makes up the lion's share of the roughly $50 million in mayoral campaign ads that have hit the airwaves in the pricey New York media market.
Bloomberg's poll numbers took a minor hit late last year after he persuaded New York's city council to overturn the term limits to allow him to run for a third term this November - but his $33 million outlay has been followed by a massive 33-point advantage among independent voters, according to the new Marist poll. The survey suggests that Bloomberg is also leading overwhelmingly among Republicans, and splitting the Democratic vote with Thompson. The survey indicates a racial divide, with white voters backing Bloomberg by a margin of greater than 2-to-1 margin, African-Americans supporting Thompson by 23 points, and Hispanics backing Bloomberg by 18 points.
Three-quarters of likely voters questioned in the poll say they are strongly committed to the candidate they are backing.
Bloomberg has captured the endorsement of all three of New York City's major daily newspapers, the Times, Post and Daily News. The Spanish-language daily El Diario La Prensa endorsed Thompson.
The Marist College poll was conducted October 26-28, with 524 likely New York City voters questioned by telephone. The survey's sampling error is plus or minus 4.5 percentage points.
–CNN Political Producer Rebecca Sinderbrand contributed to this report
Follow Paul Steinhauser on Twitter: @psteinhausercnn