Ritchie's deflected strike in the 27th minute secured all three points for the hosts but Rafa Benitez's side were forced to endure a nervous finish with Tom Ince and Darren Bent missing good chances for eighth placed-Derby.
Victory lifts Newcastle, winners of three of their previous four games, two points above second-placed Brighton & Hove Albion, who travel to Brentford on Sunday, in the second-tier Championship.
Reading remain third after twice coming from behind in a 2-2 draw away against Ipswich Town with Jordan Obita rescuing a point with his 78th-minute strike.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
Cameron Jerome scored the only goal as Norwich City, winners of three successive games, climbed to seventh with a 1-0 victory at Cardiff City while Bristol City ended a 10-game winless run with a 2-1 win against bottom-of-the-table Rotherham United.
Blackburn Rovers beat Queens Park Rangers 1-0, Birmingham City were 1-0 victors against Fulham, Burton beat Wolves 2-1 and Barnsley and Preston North End finished goalless.
Nottingham Forest host Aston Villa in the Championship's late kick-off while fourth-placed Leeds United visit fifth-placed Huddersfield on Sunday.
(Reporting By Tom Hayward; Editing by Clare Fallon)
