The 21-year-old Indian battled past his British opponent 7-6(5) 6-7(3) 6-2 and booked a last-four berth in the USD 50,000 hard court event.
After an intense battle in the first two sets, Ramkumar broke early in the third and staved off three break points in the second game to pull away. That lead stayed with him throughout and he served out the match in the seventh.
It took 214-ranked Ramkumar two hours and 36 minutes to subdue his opponent, ranked 260 in the ATP singles list.
"I started with a break in the third. I was down 0-40 in the second but I held. That was a big game for me. I got another in the middle of the set and finished it off at 5-2."
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Playing away from home, tennis players hardly get fan support but Ramkumar surprisingly found a few Indians in the stand cheering for him.
The Indian next faces American Mitchell Krueger, ranked 267, who reached the semi-finals after defeating Japanese Hiroki Moriya 6-3 7-6(6).