Brentford manager Martin Allen's managed to secure Pratley's services on a five-month loan deal and the deadline day signing underlined repaid the Bees boss' persistence with a 77th-minute winner.
Brentford's 2-1 victory at the City ground propelled them to top spot in League One.
Swansea are also up near the top and were hoping to land Pratley, before missing out to Brentford.