Sergeev competed with Natalia Mikhailova on the ISU Junior Grand Prix circuit for six seasons beginning in 2000.

They won six gold medals and finished 4th three times at the JGP Final.

They changed coaches in September 2006, moving from Ksenia Rumiantseva and Petr Durnev to Alexander Zhulin.

[1] Mikhailova and Sergeev parted ways at the end of the 2006–07 season – Sergeev had sustained a number of injuries, including rupture of the outer ligaments of the ankle and a fracture, followed by a meniscus problem after he returned to the ice.

[2] Mikhailova and Sergeev teamed up again in 2008 but they retired from competition after finishing 6th at the 2009 Russian Championships.