The station's 6-9am show presented by Jamie Theakston and Harriet Scott recorded a weekly reach of 893,000 in the first three months of the year.
Their nearest rival - Neil Fox on Magic 105.4 - had 831,000 listeners weekly, only just ahead of Capital 95.8's breakfast offering.
Capital brought in Denise Van Outen to join Johnny Vaughan for its morning show in February. During the 6-9am period the pair reached 829,000. They are on air until 10am, and their reach including the final hour was 943,000.
Meanwhile, the London audience of Christian O'Connell's breakfast show on Virgin Radio has shown particularly rapid growth.
The programme's weekly reach for the first quarter was 625,000 - a 9.1% increase year-on-year and 3.5% up on the previous quarter.
David Lloyd, Virgin's programme and marketing director, said O'Connell was "building on his ever increasing popularity".