Currently, Ruto's Kenya Kwanza leads the Azimio by one seat in a tally of 161 to 160, and the victory in other seats could inform the coalition that will win the coveted positions of Speaker and Deputy Speaker, Majority Leader, and Majority Whip in the National Assembly.
If the Supreme Court upholds Ruto's victory, he will want control of the National Assembly to ensure his government business is expedited.
In the two weeks since he was declared winner by IEBC chairman Wafula Chebukati , the president-elect has gone on the charm offensive, welcoming nine of the 12 independents and wooing MPs from other parties to join him.
On Friday, Ruto welcomed Ugenya MP David Ochieng and his MDG party to the Kenya Kwanza coalition days after he won over the United Democratic Movement of Mandera senator-elect Ali Roba, an Azimio affiliate, that has six members in the National Assembly and two in the Senate, to his fold.
Alongside the four constituencies' polls, IEBC will today also conduct elections for the governor seats in Kakamega and Mombasa and MCA posts in Nyaki West (North lmenti Constituency, Meru County) and Kwa Njenga (Embakasi South Constituency, Nairobi County).
Because of the ongoing scramble for seats in the National Assembly, parliamentary seats are more competitive than governor contests.
The parliamentary elections that Ruto and Raila will be watching closely are not only for bragging rights, but also because they will control House business.
"Parliament is different because they have to elect the speakers and then deal with contentious issues that will affect the running of government," political analyst Prof Macharia Munene says.
Kenya Kwanza is backing Bungoma senator Moses Wetangula while and Azimio is fronting Wiper leader Kalonzo Musyoka, and every vote in the National Assembly will count.