Aro Muric was Nottingham Forest’s fall-guy as two errors from the debutant goalkeeper ushered West Bromwich Albion towards a winning start and boosted Slaven Bilic’s bargaining power to bring in four more new players before Thursday’s transfer deadline.

Forest’s new 6ft 6in goalkeeper, on loan from Manchester City, allowed Kyle Edwards’ shot to go under his body and Matt Phillips’ speculative cross-shot into the top corner.

The new West Brom head coach, who has signed five players this summer, believes his squad needs replenishing after Craig Dawson, Salomón Rondón and Jay Rodriguez led the exodus since the Championship play-off semi-final defeat by Aston Villa.

Forest had made a brilliant start, meriting the lead gained through Matty Cash’s eighth-minute shot, but never recovered from West Brom’s two quick goals.

Both these clubs are on their third manager of 2019, rendering stability a distant prospect, but Bilic urged his board to build on this winning start.

“We are good, but I said to the board it would be a shame if we do not finish the business,” he said. “At the moment, we’ve only done half a job, we need quality and quantity.”

Aro Muric lets Kyle Edwards’ shot slip through his grasp for West Brom’s equaliser. Photograph: JMS Photography/Rex/Shutterstock

West Brom have been linked with FC Basel striker Albian Ajeti and Sporting Lisbon winger Matheus Pereira, and Bilic also wants another central defender, with Ahmed Hegazi ruled out for a lengthy period after ankle surgery.

Bilic added: “We have lost eight regular players, eight good players, from last season but we have gained four so we need four more. Hopefully we’re going to get them. It’s not easy but we have to do it. I was told we have the money; we’ve sold the players for good money so we should have it.”

Forest fans have become accustomed to welcoming new managers but there was a great buzz around the City Ground in the early stages as Sabri Lamouchi’s team got off to an ice-cream start: lovely at first but soon melting in the August heat.

With four of Forest’s eight new signings making their debuts, there was an immediate indication of the way Lamouchi wants his side to play out from the back.

Muric fed Ben Watson then took the return and chipped his next pass into Tiago Silva beyond the press. Eventually this led to Cash attempting a one-two with Albert Adomah onto which the versatile right-back was allowed to advance to the edge of the penalty area before walloping home at the near post.

But West Brom took control after Muric’s two mistakes. Firstly Edwards cut in from the left before producing a lovely dummy that seemed to wrong-foot the entire Forest defence. Going back outside Cash, the winger struck a shot without too much apparent power only for the ball to go underneath Muric’s dive.

The Kosovo international was again embarrassed as West Brom took the lead in the 26th minute. Phillips appeared out of harm’s way when shaping to cross from near the touchline. With Jack Robinson attempting to intervene, the ball’s looping trajectory put Muric off but he should still have done better as the ball fell into the far top corner.

Lamouchi, the new Forest head coach who succeeded Martin O’Neill in June, said he is willing to “bet he will not make two mistakes in one game again”.

“It was a very difficult start and a very difficult game for him but I trust him. He has a lot of quality, will add to us a lot this season and play a fantastic game next or in the future.

“When you have fantastic young players, they have a lot of quality and sometimes they make mistakes.”