Managed by former Manchester United star Wayne Rooney, Plymouth arrived at the Hawthorns looking for another scalp after their shock win against previous leaders Sunderland last week.
But Maja's 62nd-minute strike ensured Rooney would go home empty-handed this time as West Brom remained one point clear at the top in the race for promotion to the Premier League.
Second-placed Sunderland bounced back from that loss to Plymouth with a 1-0 win over local rivals Middlesbrough at the Stadium of Light.
Chris Rigg, 17, scored in the 24th minute with an outrageous back-heeled strike.
Third-placed Burnley left it late to beat winless Portsmouth 2-1 at Turf Moor.
After Callum Lang fired Pompey into a half-time lead, Jeremy Sarmiento made an instant impact off the bench just after the hour mark before Josh Brownhill netted four minutes into added time.
Gustavo Hamer's fourth goal of the season lifted unbeaten Sheffield United up to fourth place with a 1-0 success over Derby at Bramall Lane.
Norwich thrashed Watford 4-1 at Carrow Road, while promoted Oxford's fine start was halted by a 2-1 defeat to Bristol City at Ashton Gate.
Largie Ramazani scored on his first start for Leeds in a 2-0 victory at Cardiff as Daniel Farke's side climbed to sixth place.
The winger netted on the half hour, nine minutes after Joel Bagan was sent off for City, before Jak Alnwick saved Leeds defender Pascal Struijk's penalty in the 67th minute.
The visitors made certain of the points when former Swansea forward Joel Piroe scored two minutes from time.
Swansea beat Coventry 2-1 at the CBS Arena, while Luton came from behind to defeat Sheffield Wednesday 2-1 at Kenilworth Road.
The Owls were winning 1-0 in the 77th minute when Di'Shon Bernard conceded a penalty and was sent off, with Carlton Morris converting from the spot and then netting the winner two minutes from time.
Duncan Watmore scored his fifth goal of the season in Millwall's 1-1 draw at QPR.
The former Middlesbrough forward struck in the 34th minute at Loftus Road, six minutes before Michael Frey equalised for the hosts.
