Came across this in an e-mail earlier for Greenwich card holders. Similar offers previously did not need the card - the ticket should suffice - and the TM website mentions partner offer so it's not specific.
EDIT: as Jerry-Co mentions there is no mention of needing to take the card on the greenwich site:http://www.greenwich.gov.uk/Greenwich/LeisureCulture/GreenwichCard/O2TicketsWithGreenwichCard.htm
"Watch top tennis stars play Barclays ATP World Tour Finals at The O2 from Monday 22 November to Wednesday 24 November 2010.
Tickets are just £1.50 each, plus £2.25 booking fee (per booking). What's more, tickets are TicketFast/Print at home, so simply follow the link below, book the ticket, print off the PDF and bring along for scanning on entry"
More info about who is playing and when:http://www.barclaysatpworldtourfinals.com/