Terry Flanagan closed in on a money-spinning unification showdown after beating Petr Petrov on points to successfully defend his WBO lightweight title for the fifth time at the Manchester Arena.

Flanagan was given a good work-out by his experienced Russian opponent before coming on strong in the second half of the contest to claim a 116-112, 120-108, 118-110 victory on the judges' cards.

Now Flanagan will hope to land a high-profile clash with either Ukrainian star Vasyl Lomachenko or Anthony Crolla's recent conqueror, Jorge Linares.

He would go into any such contest having learned much from his gruelling battle against the Russian, who has been around the top level since losing a brave challenge to Marcos Maidana in 2011.

Petrov certainly gave Flanagan problems in the early stages but the Manchester man's sharper work began to prevail and he visibly rocked his opponent with a stiff one-two in the ninth round.

Petrov was clearly not going anywhere, and continued to bull forward into the last in a vain attempt to convince the judges that he had done enough to wrest the title from the home favourite's hands.

Terry Flanagan celebrates beating Petr Petrov to retain his WBO lightweight title (Getty)

Earlier, Liam Smith claimed a controversial victory over domestic rival Liam Williams after the Welshman was withdrawn before the beginning of the 10th round due to a serious cut to his eyelid.

Williams appeared to be winning the bout, which was nominally for the WBO interim super-welterweight title, although Smith did not win it as he scaled two points over the limit at Friday's weigh-in.

The premature ending after an engaging contest led to protests from Williams' corner that the bout should have gone to scorecards because the injury was caused by an apparent head-butt.

Williams was pulled out of the fight after appearing to suffer a large gash in a clash of heads (Getty)

At the time of the ending Smith had appeared to be clawing his way back into the contest after the sharper and brighter work of his previously unbeaten opponent saw him build up a commanding lead.

Promoter Frank Warren admitted he wanted to see an immediate rematch - although it remains to be seen whether the WBO will sanction Smith again after his failure on the scales.

Asked about a rematch afterwards, Warren said: "There's got to be. It was a great fight - Liam Williams started well and Liam Smith was coming back at him when it was ended."