Yadav had booked his ticket to London by running his career best 2:16:59 in January 2012, but later could not come anywhere near that time in much cooler conditions in Olympics.
Singh, who is also from the Army like Yadav, is going into the race with his confidence boosted by his personal best time of 2:22:30 clocked in the Eindhoven Marathon last year.
But he has to contend with not only the two-time (2009 and 2012) Indian topper Yadav but also with another seasoned marathon runner and three-time topper (2010, 2011 and 2013) Binning Lyngkhoi, with 2:18:47 as his career-best time.
Incidentally, Ram Singh skipped last year's race while the other four were overtaken by Karan Singh.
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There are incentives, apart from the prize money, declared yesterday by the Athletics Federation of India (AFI) and Tata Consultancy Services to further motivate the Indian runners.
AFI has made it as the pre-qualification race for the World Championship in August by keeping the qualifying standard as 2:18 for men and 2:44 for women.
The women's race could be a toss-up between experienced steeple chasers and Asian Games medallists Lalita Babar - the defending champion who won a bronze at the 2014 Games in Incheon - and 2010 Asiad gold medallist Sudha Singh.
Then there is O P Jaisha - 1,500m Incheon Games bronze medallist and 2006 Doha Asiad 5,000m bronze medallist - to look out for in her maiden attempt at the race, along with last year's second-best (among Indians) finisher Vijaymala Patil.