While playing tennis for Lincolnshire, he first came into international prominence when he reached the finals of Le Petit As, Tarbes.

Although he came across little success initially, he finally qualified for a Futures event in Portugal before losing in the first round to an ATP top 500 player.

Cox advanced to the second round of the Australian Open Boys' Singles championship before losing to Roman Jebavý of the Czech Republic.

After his defeat, Cox went to play on some more Challenger tours reaching the semi-finals in Binghamton before losing to Sergiy Stakhovsky.

At Binghamton, Cox won his first ever title at Challenger level, teaming-up with fellow Brit Daniel Smethurst to win the Doubles, defeating Stakhovsky and Marius Copil in the final 6–7, 6–2, 10–6.