Salesforce.com CEO Marc Benioff Business Insider/Julie Bort Microsoft's new CEO Satya Nadella has made a fan out of one former Microsoft rival: Salesforce.com CEO Marc Benioff.

Microsoft was even the opening act of Salesforce's massive customer conference being held in San Francisco this week.

Benioff interviewed Microsoft's new Windows marketing leader, Tony Prophet, on stage. Prophet was hired away from Hewlett Packard when Nadella took office.

"A year ago at Dreamforce we would not have thought Microsoft would have been here, on stage. It's a shock," he said, to laughter from the crowd. "I'm fascinated that he chose you as the representative of Microsoft."

John Thompson, Microsoft chairman and Virtual Instruments CEO Microsoft In May, just a few weeks after Nadella took office, the two companies struck up a partnership, initiated by Microsoft. They are showing off the not-yet-ripe fruits of that young partnership at the conference which includes making Salesforce.com and Microsoft Office apps work together with new Windows and Windows phone apps.

The reason this partnership is so shocking: Salesforce.com and Microsoft have been bitter competitors in Salesforce.com's bread-and-butter market, "customer relationship management" software that helps salespeople track contacts and make sales.

That competition isn't going to end either. In fact, a Salesforce exec recently told new recruits to view this partnership like means to grab share away from Microsoft.

"We're gonna wrap our arms around Microsoft. We're gonna pretend like we're a boa constrictor. And we're gonna suck the life out of them," a Salesforce.com strategy executive told trainees last month.

That was not a sanctioned opinion by the company, who tells us,"We deeply value our partnership with Microsoft."

Clearly Benioff wanted to prove that how much he values the new partnership with Microsoft, too, with this opening interview.

Tony Prophet, Microsoft corporate vice president, Windows Marketing Business Insider/Julie Bort Prophet and Benioff are friends through their mutual love of philanthropy. Prophet is a supporter of the new Benioff Children's Hospital in San Francisco, and supports AIDs and teen education projects in San Francisco.

The soft-spoken, contemplative Prophet couldn't be more opposite than previous Windows boss Steven Sinofsky, the man who led Windows 7 and Windows 8 and was known as brilliant, but combative and authoritarian.

Benioff says he's floored that one of the first things Nadella did was hire Prophet and reach out to Salesforce.com, though the partnership may have been the brainchild of Microsoft's new chairman, John Thompson.

Thompson became chairman when Nadella was named CEO and Bill Gates stepped down from the chairman role. (Gates didn't leave Microsoft. His new title is "Founder and Technology Advisor" and he's actually more involved now than he was as chairman.)

Thompson is a well-respected leader in the tech industry, first as a high-ranking IBM exec and then as the man who turned security company Symantec into a multi-billion powerhouse. He left Symantec in 2008.

Right after becoming chairman Thompson called Benioff and suggested dinner.

"He's someone I've had a strong friendship with for 25 years in the industry," Benioff said. "Now he's the chairman of Microsoft. When I look at John, when I look Satya, when I look at you, I say, 'Wow, we have three dramatically different leaders than what has been there for decades.' To me that's the No. 1 indication that there is a new Microsoft because the people are new at the top."