Try this...
Opponent - F-15C with Aim-120C, Skill "Excellent"
Me - SU-27 , R-27ER and R-27ET
Fly on after burners. Enemy is head on.
At about 25KMs, F-15 will fire up his first missile. Don't panic, just close in your distance while maintaining a radar lock on him and monitor your RWR. When the missile has traveled 50% of its distance, fire your first R-27ER. This will make the F-15 to go defensive and he will start his missile evading techniques. Now switch to R-27ET. When there are 3 bars left in the RWR, fire your R-27ET (If no LA with ET, then fire another ER ) . When there is 1 bar left in the RWR, perform a barrel roll to out-maneuver his AIM-120.
One question... Why no ECM ?