Neither had dropped a set so far in the fortnight, and the two had spent the same average time on court.
The chasm separating their careers, however, is huge. Williams owns 10 Grand Slam titles, making her one of the all-time greats, while Dementieva, a resilient grafter, lost her only two Grand Slam finals five years ago. An Olympic gold last summer in Beijing accounts for her biggest prize.
Few, then, expected Dementieva to prevent the widely predicted all-Williams finale for the second consecutive year at the world's most famous tennis tournament.
But it almost happened.
Williams saved a match point against a big-serving (yes) and big-returning Dementieva to triumph 6-7 (4), 7-5, 8-6 in 2 hours, 49 minutes, the longest Wimbledon women's semifinal in the Open era. The drama unfolded on the fourth straight day of sweltering heat. Pretty soon, they'll be calling London the European Riviera.
"Elena played so well, and we gave the crowd a wonderful match," said Williams, who had lost to Dementieva in Beijing. "I wasn't on my game," she told a television interviewer.
Serena Williams, like big sister and two-time defending champion Venus Williams, usually saves her best tennis for the second week of majors and held an impressive 12-2 record in Grand Slam semifinals going into Thursday as proof. Serena Williams' last defeat occurred a while ago, at the 2003 French Open, to a Belgian with a greater pedigree than Dementieva -- Justine Henin. Williams also demolished fearless Belorussian Victoria Azarenka, the player regarded as the biggest threat in her half, in Tuesday's quarterfinals.
But Dementieva hung with Williams, adding weight to her 2009 tournament stats.
After striking an ace on the opening point, Williams, who claimed the last of her two Wimbledon crowns weeks after the loss to Henin, dipped.
Recovering an early break, she then blew a chance to take a 5-3 lead by squandering three consecutive break points. The crowd approved -- the brave Centre Court souls who dealt with the heat wanted a match.
Dementieva, mixing up her serve, forced a tiebreaker, in which the first five points went to the server. On two of those points, Williams uncharacteristically flubbed backhands.
The double faults Dementieva once struggled with resurfaced at 6-3, although Williams let her foe off the hook by producing an ugly forehand return wide off a meek second serve. Williams cracked her racket.
The pair conjured more unforced errors than winners in the opener, yet it was highly dramatic stuff. The second set was more so.
Dementieva rallied from a break down to forge ahead 4-3. Facing a break point, Williams showed her champion's heart by unleashing a forehand deep down the line. No out call came, Dementieva challenged and Hawk-Eye revealed the ball was good by less than a millimeter. Gasps ensued.
The gods were on Williams' side. Fast forward to 5-5, and Dementieva's short forehand clipped the top of the net at break point, curved to the left and dropped, seemingly on the line. This time Williams challenged, a rarity for her, and further gasps flowed -- she was right.
Four break points to force a second tiebreaker went astray for Dementieva, with Williams twice uncorking an ace. She hit 20 altogether.
Dementieva did have a chance on one of those break points, sending a backhand wide as Williams drifted out of position. She turned around, knelt and buried her face in her left hand.
An ace sealed the set, with Williams saving six of seven break points in the second.
Visibly down, Williams let Dementieva off the hook to begin the third. Two shoddy errors, from 15-0 up on the Dementieva serve, plus a wild approach, handed the world No. 4 the initiative.
And this after Williams said this week that her tactical play is overlooked.
The fierce slugging continued as Dementieva manufactured a match point at 5-4.
Williams' fans must have shuddered when she decided to foray to the net. This time the approach was better, but Williams still almost missed, clipping the tape with a backhand volley.
"I was thinking on that point I wanted an ace," Williams said.
At 6-5 for Dementieva, Williams dug out of a 0-30 hole, her serve coming to her rescue. Thunderous groundstrokes were exchanged, and Williams floored Dementieva thanks to a crushing cross-court backhand that clipped the baseline. It went to 6-6 on a wonderful forehand cross-court pass, precipitating a fierce fist pump.
Dementieva sank, Williams broke to reach Saturday's final and Centre Court caught its breath.
Ravi Ubha is a frequent contributor to ESPN.com.