Katy Perry's lead over Lady Gaga in the US singles chart is set to widen.

Both acts released comeback singles recently, with the former unleashing 'Roar' and the latter debuting 'Applause'.

They were expected to have a tense and close battle in the Billboard chart, but Perry was installed as an early leader.

New figures now estimate that 'Roar' could shift up to 550,000 copies in its first week, with 'Applause' projected to sell up to 225,000.

The single is expected to give Perry her best ever first week results, beating the 509,000 sales of 2010 song 'Firework'.