Marenko stayed on resolutely to lift the Group Three Betfred TV Fred Darling Stakes at Chelmsford.
Trained by Richard Hannon and ridden by Ryan Moore, Marenko was sent off a 5-2 shot after showing up well in Group company on more than one occasion last year.
Winner of a Kempton conditions event earlier this month, Marenko kept on with real purpose to seize the lead with around a furlong to go in the seven-furlong heat, eventually pulling clear of Light Up Our World.
Besharah was sent off the 2-1 favourite and she eventually finished third.
Hannon said: "I think the trip was a little bit on the short side for her as she's done very well from two to three and she's a scopey filly with a lovely attitude.
"We took her out of the Guineas as we thought about looking at a Listed race at Royal Ascot, but that's now obviously not the way forward, so we will sleep on it and see where we go from here.
"Maybe towards the end of the year she might be a Sun Chariot type and she may be one for the Falmouth Stakes at the July meeting but she's done plenty for now and I'm happy to leave her for a bit."
Hannon also trains Light Up Our World and he expects her to shine over further.
He added: "The second will improve massively for going up to a mile and a quarter, but she's not quite there in her coat yet. They are two lovely fillies."
Tasleet got the better of Knife Edge in a thrilling finish to the Betfred World Snooker Starts Today Greenham Stakes.
The William Haggas-trained colt was sent off the 4-7 favourite in the hands of Paul Hanagan after winning a competitive sales race last year before being touched off at Group Three level on his final start of 2015.
Tasleet threw away any chance of victory that day by drifting across the track, but he kept a straight line this time as Knife Edge served it up to him in the final furlong.
Tasleet and Knife Edge were neck and neck in the dying strides, but the first-named just prevailed in a photo finish.
Haggas said: "He's still a very genuine and kind horse. Paul said he was uncomfortable as he was leaning to the right the whole way round.
"He stuck on well and I thought he was going to get done on the line, so I'm relieved.
"I think we will see what (owner) Sheikh Hamdan (Al Maktoum) has in the Guineas.
"I'm not sure he will be better at a mile myself and there's a strong possibility we will aim him at the Jersey or the Commonwealth Cup (at Royal Ascot). I think a stiff six furlongs where they go flat out will be fine."
Knife Edge's trainer Marco Botti now has a European foray in his sights for his charge.
He said: "He's run well and I'm delighted with him. Ryan Moore liked him and said he probably wants an extra furlong.
"He's an inexperienced horse and I'm sure he will improve again. He's a horse that will get better with time as he has plenty of scope.
"Originally I said about going for the German 2000 Guineas and I still think that will probably be his next target."
