Dean Whare made a spectacular NRL debut for Manly, scoring a genuine hat-trick with the first three tries of their win.
The tries helped Manly to an 18-0 lead before the Cowboys made all the running late in the game. Despite the hosts' late dominance, they couldn't capitalise on sixopportunities in the final 20 minutes.
Whare's opening two tries came from his first two touches of the ball. Chris Bailey created space 10m out for the opener in the fifth minute while the second was a raw wrestle to get it down amid a mass of Cowboys tacklers in the 11th.
The third came in the 25th minute from the remnants of a bomb as the ball spilled out the back on the line. Whare almost had a fourth when he ran off the shoulder of second rower Anthony Watmough but instead passed for winger Michael Robertson to score.
The Rotorua-born back transferred to the Sea Eagles from the St George-Illawarra Dragons in November and is known as the second-fastest man in the senior squad next to now-injured fullback Brett Stewart. He demonstrated that pace but also showed plenty of defensive clout as well.
Halfback Johnathan Thurston brought the Cowboys back into the match after they trailed 24-6 at the break, although his conversion record of 25 straight was broken by two misses.
Thurston was helped by a storming run from former Warriors prop Leeson Ah Mau to set up Ashley Graham for his second try with a perfect release in-field as he went into touch in the 62nd minute.
They then missed opportunities in the 64th, 66th, 68th, 70th, 75th and 80th minutes as they peppered the Sea Eagles with kicks and broke their line.
Cowboys 20 (A Graham 2, W Tupou, L O'Donnell tries; J Thurston 2 goals) Sea Eagles 24 (D Whare 3, M Robertson tries; J Lyon 4 goals). Halftime: 24-6.
