The holders ran out deserving three-point winners (1-12 to 0-12) over their West Mayo neighbours, Ballintubber, with Mayo star Richie Feeney plundering the all-important goal.
However, the match finished controversially as Cillian O’Connor had a Ballintubber goal ruled out ten minutes from time.
O’Connor’s flicked goal, had it stood, would have left just one point between the teams but referee Eamonn McAndrew was informed by a linesman that Ballintubber had 16 players on the field at the time.
He promptly disallowed the score, and Castlebar went on to close the game out.
Both teams were without their Mayo midfield talismen as Castlebar’s Barry Moran (knee) and Ballintubber’s Jason Gibbons (ankle) sat the game out.
Last year’s beaten county finalists, Breaffy, powered to a comprehensive victory over Aghamore. Damien Mulligan’s side finished up 2-14 to 0-11 winners with impressive wing-forward, Rory Martyn, scoring superb goals in each half.
Brothers (and Mayo panellists) Aidan, Seamus and Conor O’Shea all lined out for Breaffy, with Seamus producing a man of the match display at midfield.
However, Conor’s day came to a premature end after being red-carded for striking in the closing minutes.
Breaffy were always incontrol of the match but Aghamore will rue a missed penalty by Alan Freeman in the 42nd minute.
The Mayo forward saw his powerful kick strike the post and rebound to safety, and Breaffy made the most of the let-off.
In a repeat of the 2005 Mayo SFC final, Shrule/Glencorrib and Crossmolina played out a thrilling draw (1-8 apiece).
Former Mayo All Star Ciarán McDonald, who has come out of retirement to line out with Crossmolina again this season, hit three points and treated the crowd to an exhibition of passing and shooting.
However, he was powerless to prevent the North Mayo side squandering a seven-point half-time lead as Shrule/Glencorrib grabbed a share of the spoils.
A goal from All-Ireland winning Mayo minor Fionán Duffy put Crossmolina in the driving seat at the interval but former Mayo attacker, Mark Ronaldson, converted a late penalty to snatch the lead for the home side.
There was still time for one more twist though and Declan Keating popped up to land the equalising point.
Westport pipped last year’s semi-finalists Charlestown by 0-11 to 0-10 on Saturday evening. Lining without two-time All Star Lee Keegan, who had tonsillitis, the West Mayo side prevailed thanks to a late winner from substitute Martin Gill.
There were also wins for Garrymore over Ballinrobe (1-12 to 0-8 with Mayo forward Enda Varley scoring the goal), Knockmore beat Kiltane in Bangor (3-16 to 1-16), Ballaghaderreen overcame Davitts (1-12 to 0-10) and Claremorris hammered Ballina (0-16 to 1-2).
Second round games take place in four weeks’ time.