Belgium's Tom Boonen, riding for Omega Pharma-Quick Step, won the fourth stage of the Tour of Qatar on Wednesday, a 147km ride from Al Thakira to Madinat Al Shamal, as he tightened his grip on the race leadership. Boonen won a sprint finish to see off Dutchman Tom Veelers and Swiss Fabian Cancellara. Thursday's fifth and penultimate stage is a 160km ride from Camel Race Track to Al Khor.