Over the next 86 seconds, Varthaman and his adversaries dodged and weaved as missiles whistled through the air.
Pakistan's fighter group included eight F-16s, four French Dassault Mirage-IIIs, four Chinese-origin JF-17 Thunder fighters and at least one Saab 2000 Erieye early warning and control platform.
The IAF scrambled a combat air patrol comprising two Russian Sukhoi Su-30 fighters, two upgraded Mirage-2000H's and four upgraded Soviet-era MiG-21 Bison aircraft.
Indian military sources said the IAF joined the battle after three Pakistan Air Force F-16s crossed the border and discharged laser-guided missiles at the Nowshera munitions depot, 8km inside Indian territory, but missed their target.
Varthaman aimed to position himself at an angle of 60 degrees to the F-16 in his sights, an "angle of attack" that would enable him to execute a missile strike, the sources said.
The F-16 pilot, flying at more than 900km/h, went into a steep ascent, climbing to around 26,000ft before hurtling back down in a move to shake off his pursuer. Varthaman positioned his MiG-21 behind the F-16 and fired his Russian short-range Vympel R-73 air-to-air missile at the F-16, scoring a hit.
But within moments Varthaman's fighter was incapacitated by one or possibly two air-to-air missiles, forcing him to eject and parachute down. He landed in Pakistan-administered Kashmir. A crowd of villagers gave chase until he stumbled into a nearby shallow stream. He was shot in the leg and handed to the Pakistani authorities.
Pakistan and India have been to war four times since 1947 but the aerial combat was the first between nuclear-armed states and the first between the air forces in 48 years.
The latest rise in tension started with a suicide bomb attack by Pakistan-based jihadists that killed 40 Indian troops. India retaliated with missile strikes at a militant base on the Pakistan side.
Varthaman was returned to India. However, the identity of the PAF pilot, his fate and his F-16 remains shrouded in mystery. India exhibited pieces of the downed PAF fighter that they say had fallen into Indian territory, but Islamabad has yet to own up to its loss.