Meanwhile Nottingham Forest lost the East Midlands derby in a 3-0 reverse at Leicester City and dropped down to third in the table, while Sheffield Wednesday tumbled into the relegation zone after a 5-0 thrashing at Reading.
Substitute Will Hoskins' 90th-minute consolation goal for the Hornets could not prevent the Magpies from extending their lead at the top of the second-tier Championship to six points.
West Bromwich overtook Forest to reclaim the second automatic promotion spot, going two points above the former European champions.
Forest are now eight points behind Newcastle with a game less to play than both the Magpies and WBA.
Three goals in the last 25 minutes finished them off before 31,759 fans at the Walkers Stadium -- the Championship's biggest attendance of the day.
The Foxes' victory leaves them in fifth place, nine points behind West Brom and the second automatic promotion spot.
In the battle to avoid relegation to the third-tier League One, rock-bottom Peterborough's defeat left them 10 points from safety.
Sheffield Wednesday were hammered 5-0 at the Madejski Stadium, which left the hosts four points above the drop zone, with Wednesday dipping into the bottom three on goal difference.
Crystal Palace, now in the thick of the relegation battle after having 10 points deducted for entering administration, earned a 1-1 draw at Doncaster in what could be manager Neil Warnock's last game if he accepts an offer from Queens Park Rangers.
Source: AFP European Edition