The world number 43 had already accounted for top seed Agnieszka Radwanska in the quarter-finals of the WTA International hard-court event but McHale looked fresher after her last-eight clash concluded with just 10 games completed as opponent Magdalena Rybarikova retired injured.
And so it was McHale who started brighter, putting the fifth seed on the back foot by winning 72 per cent of service points in the first set.
The second was an entirely different story as Lepchenko converted all four of her break-point openings to level the match.
McHale looked to have found an extra gear in the final set, breaking twice in the opening exchanges for a 3-0 lead, and served for a place in the final at 5-4 40-30.
But Lepchenko dug deep and broke her fellow American, only to hand back the initiative immediately by losing her own serve as McHale had another chance to close out the win at 6-5.
Once again, Lepchenko fought back and was never behind in the tie-break, eventually sealing victory after two hours and 41 minutes of play.
She will now take on Karolina Pliskova, who overcame wildcard entry Maria Kirilenko 4-6 7-6 (7-5) 6-3 in another closely-fought affair.
Pliskova was unconvincing in an opening set that saw her land just 38 per cent of her first serves, a level of inconsistency that led to the Czech being broken three times.
She struggled to up that average in the second but managed to force a tie-break, where only five of the 12 points went with serve and Pliskova ultimately prevailed.
Even in the deciding set, Pliskova was unconvincing on serve but she fought hard to deny Kirilenko on four of the Russian's five break-point opportunities.
And, when it came to the crunch, it was Kirilenko who buckled, dropping her serve to love before Pliskova closed the match out.