United were the dominant side throughout the first half against Birmingham City Women and duly got their reward when Hayles swept home to open the scoring.
After coming on in the second half, Sibley guaranteed all three points with her first goal for the club when she pounced on a loose ball inside the area and beat the final Birmingham player on the line.
An even start to the match saw Birmingham fashion the first chance of the game after eight minutes when Ivana Fuso picked out Lily Agg in the box following some neat footwork, but the latter's strike sailed high over Claudia Moan's crossbar.
However, it was United who opened the scoring through Sela's October Player of the Month and the team's top markswoman Hayles.
Beth Lumsden managed to create a yard of space on the right through some quick stepovers before picking out Hayles on the penalty spot and she swept home at the first time of asking.
The hosts looked to draw level almost immediately when Fuso pounced on a loose Moan pass out from the back, but United's goalkeeper recovered well to tip Brazilian's shot around the post.
Birmingham thought they'd equalised on the half-hour mark through Agg, who saw her header hacked off the line by Charlotte Potts.
The Blues came flying out of the traps in the second half and should've clawed themselves back level, but Tegan McGowan could only direct her first-time volley narrowly wide of the far post.
Only five minutes after the restart, Birmingham continued to knock on the door - but this time Fuso's deflected cross rebounded back out off the crossbar.
In the space of two second-half minutes, Fuso could've put Birmingham ahead. First of all, the Brazilian was found in acres of space and bearing down on goal, but Moan stood tall and tipped her fizzing effort behind for a corner.
Moments later Birmingham's number 13 was once again free at the back post, but despite having time on the ball, Fuso snatched at her effort which went aimlessly over from close range.
Just as the game approached the hour mark, Birmingham went close once more. A whipped free kick reached the back post, but Neve Herron could only cannon her header off the post and watch it trickle along the goal-line.
Not even 20 minutes had been played in the second half and Amy Merricks' side had been denied by the woodwork three times. This time it was an audacious Tegan McGowan strike from 25 yards which beat Moan but rattled off the crossbar and away to safety.
Despite the non-stop pressure, it was Newcastle who sprung a counter-attack and doubled their lead.
Lumsden drove at Martha Harris down the left and unleashed a wicked strike which bounced off the bar to substitute Sibley, who took one touch before thrashing home.
It was almost double delight for Sibley two minutes later as she once again found herself unmarked in the box, but what looked to be a certain goal was deflected over by a last-ditch Birmingham block.
There was also a special moment in the 89th minute when fan favourite Georgia Gibson made her 100th appearance for the club, to go alongside the 59 goals she's scored in black and white.
Newcastle United Women: Claudia Moan, Liv Watt, Deanna Cooper, Charlotte Potts, Demi Stokes, Amy Andrews, Elysia Boddy, Lois Joel, Jasmine McQuade (Georgia Gibson 89), Beth Lumsden (Katie Barker 89), Shania Hayles (Isabella Sibley 60)
Subs not used: Grace Donnelly, Emma Kelly, Kacie Elson, Sophie Haywood, Hannah Greenwood