Keith Richards and Ronnie Wood were pictured smoking on stage during their concert at the new arena on Tuesday night.
Newspapers reported that stewards scrambled to stop onlookers from following suit, even threatening to evict those who lit up.
The law, which came into force on July 1, prohibits smoking in public indoor places. Landlords can be fined 2,500 pounds ($5,000).
More than 20,000 fans watched the ageing rockers kick off the UK leg of their latest tour, A Bigger Bang at the former Dome in Greenwich.
In a statement, a Greenwich Council spokesman said: "We have reminded the O2 of their obligation to enforce smoking legislation.
"We are satisfied with the assurances they have provided that this will not recur."
A spokeswoman for the arena said: "A band member appeared to have a cigarette. However it was extinguished almost faster than the message to put it out got to stage.
"We are sure it was an oversight and are grateful for their co-operation. Along with the rest of the country, we take the smoking ban seriously."
But a source close to the band told The Times: "Ronnie and Keith have been smoking on stage for the last three decades and they're not going to stop for the next two.
"Of course they're going to have a fag -- it's what they do.
"You might say that Keith and Ronnie lighting up while they swap licks is part of the Stones performance."
Keith Richards reissues rare single on iTunes
Dec 6, 2007 6:00 pm PST
Rolling Stones guitarist Keith Richards is reissuing his 1978 solo single "Run Rudolph Run" on iTunes just in time for the holidays, his spokeswoman said on Thursday. The tune, popularized by Chuck Berry, will be sold on a two-for-one bas...
Rolling Stones' Richards joins march
Oct 27, 2007 9:00 pm PDT
Keith Richards joined about 15,000 people marching in southern England on Saturday against possible cuts in services at a hospital near his country home. The 62-year-old Rolling Stones guitarist issued a statement saying St. Richard's Hos...
Stones demand apology from Swedish papers
Aug 29, 2007 8:29 am PDT
Guitarist Keith Richards has demanded that two Swedish newspapers apologize to the Rolling Stones and their fans in Sweden for stinging reviews of the band's performance at a concert in Gothenburg. "Never before have I risen to the b...
Keith Richards Supermad over "Superdrunk" Reviews
Aug 29, 2007 2:51 am PDT
Talk all the smack you want about Keith Richards and coconut trees. Just don't bring his musical prowess into the mix. The Rolling Stones guitarist has lashed out at two Swedish newspapers that printed scathing, sobriety-challenging ...
Keith Richards: 'I DID snort my dad's ashes'
Aug 6, 2007 12:00 pm PDT
Rolling Stones guitarist Keith Richards has confirmed that he did snort his father's ashes, as he told NME.com earlier this year. Richards originally claimed he was misquoted, after his publicists attempted to quash the story. Richards, ...