The Mirror website was closing fast last month on The Sun in the latter's last month as a free website.
The Mirror was the fastest growing national newspaper website, up 85 per cent to 1.4m 'unique browsers' a day in June according to ABC.
This compares with The Sun up 18.7 per cent year on year to 1.8m uniques. The Sun goes behind a paywall as of 1 August.
Mail Online continues to be the most popular newspaper website in the UK (and the world) with 120.8m browsers a month and 8.1m a day in June, according to ABC.
The Guardian remains well ahead of the third-placed Telegraph with 85m browsers a month worldwide.
The Telegraph, despite being behind a paywall which limits free access to 20 articles per month, continues to grow year on year.
But it has seen its first month-on-month decline since going behind a paywall in April. Daily browsers were down 4.2 per cent month on month to 2.7m.
UK national newspaper website unique browsers for June 2013 (source ABC)
Daily browsers: 8,111,988, up 38 per cent
Monthly browsers: 120,829,031, up 29 per cent
Daily browsers: 4,884,043, up 44.7 per cent
Monthly browsers: 84,933,955
Daily browsers: 2,733,136, up 16.1 per cent
Monthly browsers: 54,007,113, up 18.4 per cent
Daily browsers: 1,814,963, up 18.7 per cent
Monthly browsers: 29,603,055, up 18.5 per cent
The Mirror Group:
Daily browsers: 1,440,082, up 85.2 per cent
Monthly browsers: 29,354,671, up 88.2 per cent
Daily browsers: 1,099,561, up 80 per cent
Monthly browsers: 23,577,495, up 84.3 per cent
Daily browsers: 417,551, up 16.2 per cent
Monthly browsers: 9,644,662, up 18.3 per cent
Daily browsers: 187,558, up 41.65 per cent
Monthly browsers: 4,126,393, up 40.6 per cent