Mr Pkosing defended his seat after garnering 28,225 votes to beat UDA's Simon Kalekem who got 15,298 votes. James Lopoyetum, who run on an Independent, had 2,677 votes.
The polls registered a 79 per cent voter turnout.
The Pokot South MP-elect thanked voters for defying Kenya Kwanza coalition.
"This was not an election between me and my fellow candidates in Pokot South. The saboteurs of Pokot nation had an ulterior motive. The Pokot people have shown they are independent in decision-making," he said.
Mr Pkosing faulted the President-elect and his UDA team for waging a campaign against him, saying he has reaffirmed that West Pokot is Azimio la Umoja One Kenya zone.
Last week, UDA leaders led by Deputy President-elect Rigathi Gachagua pitched camp in the region to rally voters against KUP candidates.
The MP-elect noted that KUP's victory has increased the Azimio numbers in the National Assembly.
"The celebrations are a sign of our freedom. We have ashamed the enemy and their projects," he said.
During the August 9 polls, KUP candidate won the Woman Rep seat.
It was a fierce contest between Kenya Kwanza and Azimio coalitions in the region perceived to be the stronghold of Dr Ruto.
In the presidential election, the UDA candidate garnered 109,944 votes against Raila Odinga's 63,092 votes.
UDA also won the governor and the Senate races as well as Sigor and Kapenguria parliamentary seats. The party got nine MCAs seats.
In Kacheliba constituency, Mr Lotee who served as West Pokot Governor Simon Kachapin's deputy during his first term in office, beat incumbent Mark Lomunokol of UDA after he garnered 20,073 votes. Mr Lomunokol, who was seeking a third term, got 17,903 votes, while Mr John Lodinyo of Kanu trailed with 1,346 votes.
In February, the Kacheliba MP-elect resigned as CEO of National Affirmative Action Fund to contest the seat.
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Mr Lotee started low-key campaigns in March.
"We have opened a new chapter to bring development in Kacheliba constituency. I want to assure my voters that I will do what I promised," he said after the win.
The MP-elect promised to shut down the Kacheliba CDF office in Kapenguria and bring it to the constituency level.
Prof Lonyangapuo said despite KUP failing to secure the governorship, the three parliamentary seats have affirmed the party's popularity in the county.
"Despite the Kenya Kwanza brigade camping in West Pokot county day and night, we have proved to them that we are independent, and we can make our own decision," he said.
He challenged the elected leaders to prove their critics wrong by initiating more development projects.
"We will continue standing with our party and in future, a presidential candidate will come from the party. I will be in the villages visiting my people," he said.
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