Williams was stricken with the injury at 5-5 in the second set after Hantuchova hit a forehand winner for a 30-15 lead. After having the calf massaged and wrapped, the two-time champion resumed playing and hobbled the next eleven minutes before a rain delay of nearly two hours.
When the rain came, the seventh-seeded Williams was up a set but trailed 4-2 in the second set tiebreaker.
When play resumed, Williams, sporting white leggings, lost the first five points but then began to move better and hit more aggressively. At the same time, Hantuchova's game became erratic. She committed 28 unforced errors to Williams' 21.
Williams will face Justine Henin in the quarterfinals. The top-seeded Henin beat Patty Schnyder in straight sets.