ALBION could not spoil Harry Redknapp's homecoming as their four-game unbeaten league run came to an end in a scrappy 1-0 defeat at Fratton Park.
Super-sub Svetoslav Todorov fired the only goal of the game in the 56th minute as Portsmouth closed the gap on the 17th-placed Baggies to three points at the wrong end of the table.
The visitors, who had fired eight goals in their last four Barclays Premiership outings, failed to find a way through Pompey's watertight defence to leave them still searching for their first league away win this term.
Bryan Robson made one enforced change, with Martin Albrechtsen replacing Steve Watson, who failed to shake off a hamstring injury.
The game also came too soon for Zoltan Gera (groin) but Diomansy Kamara returned to Fratton Park for the first time since joining the Baggies in the summer.
Albion controlled the first half for long periods but were unable to seriously test Pompey keeper Jamie Ashdown.
The first action saw Junichi Inamoto latch onto Matthew Taylor's clearance from Kamara's corner in the fourth minute, only for the Japan international to blaze his volley over the bar.
Two minutes later, Redknapp was forced into a change as Todorov replaced the injured Vincent Pericard.
Richard Hughes then almost played Todorov in over the top in the hosts' first real attack but Neil Clement was on hand to clear the danger.
Moments later, Curtis Davies had to be alert to prevent Todorov getting on the end of Gary O'Neil's centre inside the six-yard box.
At the opposite end, Kanu superbly controlled Tomasz Kuszczak's long punt and found Ellington on the edge of the area, but the £3million striker's curling effort lacked the pace to beat Ashdown low down.
Davies made another crucial block in the 32nd minute as he prevented Taylor from getting a shot on goal from ten yards after the recalled Laurent Robert had picked him out with a pass from the left.
Portsmouth came within inches of taking the lead three minutes later when Robert, who scored at The Hawthorns from a similar position in August, shaved the top of the net with a dipping free-kick.
But it would have been rough justice on Albion as the chance came about from a strong-but-fair challenge by Paul Robinson on Lomana LuaLua, which referee Mark Halsey deemed to be a foul on the edge of the box.
Davies came to the visitors' rescue again eight minutes after the break to deny Todorov a golden opportunity as the ball broke for the Bulgarian international inside the box from Taylor's challenge.
Two minutes later, Kuszczak pulled off a superb double save, first diving low to his right as LuaLua spun Clement to unleash a vicious effort and then bravely blocking Todorov's follow-up.
But it was only a temporary reprieve as LuaLua got the wrong side of Clement out on the right from Linvoy Prmius' long ball and cut inside to find Todorov, who deftly lifted the ball over Kuszczak to open the scoring in the 56th minute.
Pompey immediately pulled all their men behind the ball to stifle Albion's search for an equaliser - and Robson's men struggled to break them down.
The Baggies spent the rest of the game camped in Pompey's half but simply could not find a way through to test Ashdown.
In fact, it was his opposite number Kuszczak who had to be brave again when he beat LuaLua to the ball on the edge of the box after the otherwise faultless Davies left his touch short from Taylor's ball down the right.
Robson made a change in the 65th minute as he brought on Rob Earnshaw for Kamara to partner Ellington in attack and opted for a 4-3-1-2 fomation, with Kanu in the hole.
Pompey continued to soak up the Albion pressure while at the other end, LuaLua whistled a ball across the face of the Albion six-yard box in the 77th minute, but Todorov did not have the pace to meet it.
Albion kept plugging away and Ronnie Wallwork tried his luck from the edge of the area in the 89th minute, but Hughes bravely blocked his skidding shot for a corner and that proved to be the Baggies' last chance to salvage a point.
PORTSMOUTH (4-4-2): Ashdown; Primus, O'Brien, Stefanovic, Griffin; O'Neil, Hughes, Taylor, Robert; Pericard (Todorov 6 (Priske 90)), LuaLua. Subs not used: Westerveld (gk), Viafara, Cisse.
ALBION (4-4-2): Kuszczak; Albrechtsen, C Davies, Clement, Robinson; Kamara (Earnshaw 65), Wallwork, Inamoto, Greening (Campbell 90); Kanu, Ellington. Subs not used: Kirkland (gk), Moore, Carter.
GOALS: PORTSMOUTH - Todorov (56).
BOOKINGS: ALBION - Wallwork (foul 7).
REFEREE: M Halsey (Lancashire).
ATTENDANCE: 20,052.
ALBION STARMAN: Curtis Davies.
(PICS BY LAURIE RAMPLING)
