But with 1 hour 32 minutes gone, Patten and Payne made a move to try to string out the race, upping the tempo in an effort to reduce the medal contenders.
Ilchenko, however, remained in touch, as did Brazilian Poliana Okimoto and Andreina del Valle Pinto Perez of Venezuela, as the bulk of the leading group re-formed. As the swimmers went round the final buoy, however, the speed increased again and Patten and Payne's pace-making had clearly taken its toll on much of the field.
With 250 metres to go, the medal contenders were whittled down to just four, with Germany's Angela Maurer joining Payne, Patten and Ilchenko at the front.
Maurer, though, was unable to match Ilchenko's burst of pace as the Russian pulled alongside the British pair. Payne fought back, matching her stroke for stroke until Ilchenko inched ahead in the final few metres to touch first.
Patten later claimed she was unhappy with some underhand tactics during the closing stages, saying: "I was quite annoyed, it's not sportsmanship when you pull on someone's feet." But the British team have not registered an official complaint.
Looking remarkably fresh after her slog, Payne said: "It's amazing what a silver medal can do for you!
"During the race, we didn't talk at all out there. We're best friends, we train together and we just kind of knew when to kick at the right time."
Payne and Patten's success raises British swimmers' total medal haul to five at these Games, after Rebecca Adlington's two fantastic golds and Joanne Jackson's bronze.
David Davies could add another medal tomorrow when he competes in the men's 10km race.
