Ana Ivanovic’s first shot of this match was a clean return winner. On the second point of the match, Ivanovic went for an aggressive forehand down the line, which caught the net. Two points later, Ivanovic came to net to put away a ball. This was the version of the streak Serb we love to watch.

Ivanovic earned a break point that game, and I’m pretty sure I saw her opponent, Serena Williams, grimace.

Ivanovic lost that game, and Williams won the first set, 6-1.

It was not the last time momentum would quickly and unexpectedly shift in this 6-1, 3-6, 6-1 semifinal won by Williams but for a time dominated by Ivanovic.

Consider that Ivanovic returned from that opening-set shellacking to take the first four games of the second set, with an assertiveness and confidence that recalled her win over Williams at this year’s Australian Open. It had to have been difficult for Ivanovic to retain belief in her strategy after such a lopsided first set, but it paid off. Her inside-out forehand was beautiful enough for Italy's famous artists to immortalize.

Not as impressive but certainly as critical was Ivanovic’s hold for 5-2, after Serena finally sank her teeth into the set. It kept the world No. 1 at bay, and she was put away—in this set—by an unlikely Ivanovic ace.

Raise your hand if you then thought that Williams would then win the next five games.

Serving was a large reason for that. Ivanovic, who actually landed a greater percentage of first serves than Williams on the day (62 to 58 percent), was broken five times, and only mustered five total break points. Still, it was hard to imagine Ivanovic's form fizzling so drastically. But then, there are few tests as relentless as Serena Williams.

Logic was left at the door in this Roman rollercoaster that lasted just one hour and 36 minutes. But I think both players have to come away pleased, to some degree.

Williams, coming off a withdrawal in Madrid, will now go into the French Open with the confidence that her top form is still there, even if she’s had some trouble summoning it this year. She’ll also enter tomorrow’s final as a huge favorite against crowd favorite Sara Errani. Williams is 6-0 against the Italian, and their last match—last year at Roland Garros—ended 6-0, 6-1.

Ivanovic wasn’t consistent enough to win today, but proved that she can still beat the best in the world this week. She ousted red-hot Maria Sharapova in the third round, scored a nice, three-set win over clay-courter Carla Suarez Navarro in the quarters, and took a set from Serena today. That’s invaluable knowledge the former French Open champion can call upon next week in Paris.

Nevertheless...when in Rome, try to avoid Serena Williams at the Foro Italico.