The Republican, who poked fun at his presidential campaign's financial shortcomings and his reputation as a political maverick in Saturday's appearance, led the show to its second-best overnight ratings since a December 1997 holiday episode.
NBC estimated on Sunday that when the final national viewer estimate is known later this week, it will be a little less than 12 million people. Alaska Governor Sarah Palin's appearance two weeks ago was seen by 15 million people, according to Nielsen Media Research.
The presidential hopeful made a cameo appearance at the beginning of the show, with actress Tina Fey reprising her memorable impersonation of Mrs Palin.
Mr McCain, who is trailing Democrat Mr Barack Obama in most battleground state polls, also appeared during the show's Weekend Update newscast to announce he would pursue a new campaign strategy in the closing days of the campaign.
'I thought I might try a strategy called the reverse maverick. That's where I'd do whatever anybody tells me,' Mr McCain said.
And if that didn't work, 'I'd go to the double maverick. I'd just go totally berserk and freak everybody out,' the Arizona senator quipped.
Earlier in the show, Mr McCain and Fey's Palin said they couldn't afford a half-hour campaign commercial on network television like the one Obama aired earlier this week. They said they'd sell campaign products on the QVC shopping channel instead.
Among other things, Mr McCain advertised a set of knives to cut through pork in Washington. His wife, Mrs Cindy McCain, briefly appeared to advertise McCain Fine-Gold jewellery, a play on the campaign finance law McCain authored with Wisconsin Democratic Senator Russ Feingold.
Fey's Palin advertised a set of Joe dolls commemorating Joe the Plumber, Joe Six-Pack and her Democratic rival, Joe Biden.
She also pulled out T-shirts saying Palin 2012 and announced she wouldn't be returning to Alaska after the election.
'I'm either running in four years or I'm going to be a white Oprah,' she said.
Mr Obama said on Sunday that Mr McCain was funny. Addressing supporters in Ohio, he said the performance was an example of how politicians can fight on the issues but bring civility to politics by having a sense of humour.
Mr Obama said he missed seeing Saturday Night Live - he was in a motorcade in Missouri - but caught up by watching it on YouTube. -- AP