Complex sentence: Initially Kingston-on-Thames had the upper hand both in league and cup success and in matches between the two clubs, but gradually Old Kingstonians improved, winning the West Surrey League in 1910, followed by the Surrey Senior Cup in both 1911 and 1914.
Split into simpler sentences: Initially Kingston-on-Thames had the upper hand both in league and cup success and in matches between the two clubs. Gradually however Old Kingstonians improved, winning the West Surrey League in 1910, followed by the Surrey Senior Cup in both 1911 and 1914.