World number one Djokovic was untroubled as he beat Jeremy Chardy 6-1 7-6 (2) to set up a clash against Marin Cilic after the Croatian battled past Serbian Laslo Djere 4-6 6-3 6-2.
Romania's Halep will overtake Naomi Osaka at the top of the rankings if she wins the title.
Friday's victory over Bencic avenged two consecutive defeats to the Swiss.
Bencic worked a set point in the 12th game, only to see Halep fire off a couple of winners to hold, and they headed to a tie-break.
The second set began in similar fashion, a break apiece, but this time, it was Bencic who looked the bolder, stronger and more creative with her tactics. It was one-way traffic as her challenge petered out. She broke again, 5-2, and served out the set in a scant half hour, 6-2, having won 15 of the last 17 points.
Osaka will achieve both of those goals if she makes it through to the quarter-finals this week, while Simona Halep must win the title to have any chance of replacing her.
That was the second time Bertens beat Halep in a WTA final following her at the Western & Southern Open in the United States of America in August 2018.
Djokovic had battled against Austria's Dominic Thiem to win 7-6, 7-6 and progress in the Association of Tennis Professionals World Tour Masters 1000 event. "I wanted to win this match so much because she'd beaten me before - I didn't want to lose twice in a row", said the 21-year-old. Stephens had no trouble getting past Petra Martic in her last-eight encounter. He lost in the last four in both Monte Carlo and Barcelona, arriving in Madrid without winning either tournament for the first time since 2015. With this victory, Belinda made it 5-0 against the top-5 players on the WTA leaderboards in the 2019 season. She returned with a renewed sense of goal, passion, and perspective, and the result has been a meteoric rise through the rankings and transformation into an all-court threat. I played like stupid today, everything that she liked.
However, she admitted that knowing her top WTA ranking could possibly be in danger after failing to reach the Madrid semi-finals might have played on her mind mid-match on Thursday.
"I am extremely disappointed to have my time in Madrid end in this way".
And so the mighty Romanian maintains her assault on reclaiming not just the Madrid title but the No1 ranking.