West Brom's stuttering home form continued as they were forced to hang on for a goalless draw at home to fellow promotion hopefuls Sunderland.
They were indebted to several impressive saves by goalkeeper Russell Hoult to keep Sunderland at bay while Black Cats debutant Stewart Downing hit the woodwork.
Sunderland made a bright start but struggled to create any chances, while at the other end Paul Robinson saw his 25-yard shot blocked by Gary Breen.
Black Cats striker Kevin Kyle was next to threaten but his well-struck shot was held by Hoult.
Jason Koumas also had a shot saved by Sunderland keeper Mart Poom while Kyle headed wide from a Darren Williams corner as the action swung from end to end.
Sunderland went close to breaking the deadlock when Hoult needed two attempts to hold on-loan Middlesbrough winger Downing's shot from the edge of the area.
Poom was called into action again when he brilliantly tipped a Lee Hughes effort over the crossbar and the striker's frustration boiled over when he was booked for a foul on Arca.
Sunderland were looking slightly the better side though and went close when Hoult kept out Marcus Stewart's header from Downing's cross.
West Brom boss Gary Megson made a double substitution at half-time, with Hughes and O'Connor coming off to be replaced by Scott Dobie and Artim Sakiri.
But the home side needed a goal-line clearance by former Sunderland defender Bernt Haas to deny Stewart the opening goal while Hoult produced a flying save to keep out Kyle's header.
It seemed only a matter of time before Sunderland broke the deadlock, with Kyle twice testing Hoult and Arca firing over from the edge of the area.
Their best chance of the game came in the 76th minute when Hoult was finally beaten by Downing's 20-yard drive only for the ball to rattle the woodwork.
West Brom: Hoult, Gilchrist, Gaardsoe, Gregan, Robinson,
Koumas, Johnson, O'Connor, Haas, Hulse, Hughes. Subs: Murphy,
Clement, Dobie, Sakiri, Volmer.
Sunderland: Poom, Arca, McCartney, Breen, Williams, Downing,
Healy, Whitley, Oster, Stewart, Kyle. Subs: Wright, Tommy Smith,
Ingham, Thirlwell, Bjorklund.
Referee: C Penton (Sussex).