Cretskens maintained his lead of more than two minutes on the final stage as the Quick Step team dominated the week of cycling.
Friday's stage saw a breakaway after just 15km by Kenny De Haes of Belgium, Denmark’s Glenn Bak and Frenchman Emilien-Benoit Berges, who built up a seven and a half minute lead.
However the peloton worked hard and caught the leaders with 10km to ride on Doha's picturesque corniche, setting the race up for an exciting sprint finish.
Sprint king Boonen yet again pipped his great Italian rival Alessandro Petacchi, who sneaked home in second place ahead of Australian Graeme Brown.
Cretskens didn't need to sprint to the finish as he had done enough to keep the race leader's gold jersey, 2:09min ahead of Boonen who was second overall, with Dutchman Steve De Jongh in third a further 35sec behind