Guardian.co.uk's number of unique users grew by 4.14% to 27,324,309 month on month, whereas Telegraph.co.uk's unique users plummeted 13.83% to 23,875,251.
Bucking last month's growth trend the number of UK users visiting the Guardian's website fell from 10.67m in March to 9.7m in April.
Emily Bell, director of digital content at Guardian News and Media, said: "This was a great month for us, a global uplift of four per cent, pushing us 3.4m users ahead of our nearest rival. Our G20 coverage clearly played a key part in our success.
"We remain the most popular UK newspaper site too with 9.6m UK uniques compared to 8.1m from the Telegraph who are next in line."
Telegraph.co.uk's unique users fell 13.83% to 23,875,251, making it the biggest faller of all the papers' websites. The paper's big MPs expenses exclusive this month is likely to give a big bump in the next set of ABCe figures.
The Telegraph's UK users fell from 9.26m in March to 8.13m in April.
Mail Online, which includes the Daily Mail and Mail on Sunday sites, remained in third position, with the number of users falling 2.59% between March and April, to 23,153,003. Its UK users fell from 7.24m in March to 6.95m in April.
Also maintaining its position, Times Online came fourth in the ranking -- the title's online audience fell marginally (by 0.13%) to 21,585,569 users. Close on its heels in fifth position was The Times's News International stablemate TheSun.co.uk, with April traffic of 20,567,178 -- a fall of 3.21% compared with March.
Times Online saw its UK traffic fall from 8.13m in March to 7.55m in April while stablemate fell from 8.1m to 7.4m in April.
Independent.co.uk managed to repeat the success of its previous ABCe and grew nearly 4% to 10,432,660. Its UK traffic fell marginally from 4.34m in March to 4.11m in April.
Mirror.co.uk experienced an impressive leap in the number of users it attracted in April -- its 20.44% traffic increase marked the biggest rise of all the papers' websites. Its UK audience dropped sightly from 3.9m in March to 3.88m in April.
David Black, Trinity Mirror's group director of digital publishing, said: "With a primary focus on UK users we continue to grow a loyal and engaged audience that has genuine value for advertisers."