The Umno-led Barisan Nasional (BN) won a second by-election yesterday, largely thanks to an electoral pact forged on the basis of Malay-Muslim unity with Parti Islam SeMalaysia (PAS), its fellow opposition party.

The former ruling coalition reclaimed the Semenyih state constituency in Selangor from the governing alliance Pakatan Harapan (PH) with a narrow majority of 1,914 votes.

The win is a blow to the Tun Dr Mahathir Mohamad-led PH as Selangor state is its stronghold. Umno ceded Semenyih for the first time at the May general election.

Umno's Mr Zakaria Hanafi, 58, yesterday polled 19,780 votes against the 17,866 garnered by Parti Pribumi Bersatu Malaysia's (PPBM) Mr Muhammad Aiman Zainali, 30.

A candidate from Parti Sosialis Malaysia and an independent each received fewer than 1,000 votes each.

In last May's polls, PH took more than half the ballot in a 8,964-vote win as it swept to power nationally and took a whopping 51 of Selangor's 56 assembly seats.

There have been six by-elections since then, with Semenyih the first to see the incumbent defeated.

The result signals ebbing support for PH especially among the Malay majority which makes up 69 per cent of the electorate in the township about 30km south-east of Kuala Lumpur.

"It looks like Umno and PAS can start their seat allocation negotiations now to avoid three-cornered contests with Pakatan at the next general election," said BowerGroupAsia director Adib Zalkapli.

The two opposition parties have formed a loose alliance ostensibly to unite Malays in protest against the alleged erosion of Malay and Muslim privileges and rights under the PH administration.

The pressure they have applied has seen Prime Minister Mahathir backtrack on a promise to ratify a United Nations' pact to end racial discrimination in November, having earlier appointed an ethnic Chinese and Indian to the key roles of finance minister and attorney-general respectively.

A survey released on Jan 31 by Ilham Centre and Penang Institute showed that almost 55 per cent of Malays were unhappy with the government's handling of Malay issues and Islam. The Semenyih vote raises further questions as to whether Dr Mahathir and PPBM are still able to swing Malays to PH as it did at last year's elections.

PAS secretary-general Takiyuddin Hassan, who was at the BN election command centre, said the result affirmed PAS and Umno's cooperation.

"It is a good sign towards the unity of Muslims and Malays. We will continue this formula until the 15th general election," he said.

Having lost four contests in a row in by-elections last year, BN finally triumphed by widening its winning margin at Cameron Highlands in January, a seat where 55 per cent of voters are bumiputera.

Acting Umno president Mohamad Hasan said Semenyih was the "real test" for BN, as the Cameron Highlands parliamentary seat was theirs to defend and located in Pahang, one of two states that BN still controls.

"This is a good cooperation that has produced a good result," he said of PAS' decision to stay out of the Semenyih contest and instead back the BN candidate.

Former premier Najib Razak, who actively campaigned in Semenyih, also joined in the BN celebrations yesterday.

Eurasia Group practice head for South and South-east Asia Peter Mumford told The Sunday Times that investors would be concerned that "if PH feels under more pressure to maintain ethnic Malay support, it could tack further right in terms of economic and political nationalism".