In a 63rd edition light on big hits, the out-of-competition screening of the movie drew cheers from a packed cinema at the first major European film festival of the year, and Hawke and Delpy appeared moved by the reception.
The actors linked up with Texas-based director Richard Linklater, who directed them as young Generation Xers, an American and a Frenchwoman, in the 1995 cult hit "Before Sunrise" in which they have a brief Vienna tryst as backpackers and then go their separate ways.
In 2004, the trio made "Before Sunset" which sees Jesse, now a writer trapped in an unhappy marriage, publish a successful novel about the hours with Celine, and she searches him out when he lands in Paris on a book tour. The three also wrote "Before Midnight" together.
The film takes Celine and Jesse, who are now a live-in couple with twin girls, to a sun-kissed Greek island where he has brought the family with him to a writers' retreat.
The latest film picks up the series' trademark walking-and-talking trope, with extended single-shot scenes focused purely on the couple's fighting, flirting and philosophizing that still managed to hold the audience rapt.
But their conversations have grown weightier over time, with careers, child care, tensions over Jesse's ex-wife and teenage son, and the prospect of a move to the United States weighing on the relationship.
Delpy said it sometimes surprised her how broad the interest in the story remained considering how personal the project had become, and that she relished having a kind of time capsule of her own life.
"There's an element of time in our lives as well which is really unusual for actors and writers to be able to revisit," she told reporters. "Each segment is in the moment but within this period of time of 18 years. It's kind of special to do that as actors or writers."
Linklater said that each time they finished a picture they were ready to say goodbye for a while but that the material seemed too rich not to keep mining.
"I think I speak for the group here -- I'm sure we have absolutely no idea right now what that (sequel) could possibly be and we probably won't for like five or six years," he said.
"Usually we joke about it and then at some point our jokes become maybe a little more serious and we realise that Jesse and Celine are maybe trying to go, 'Hey, I'm at a new phase in my life, you have to deal with me.'"
Hawke, sporting platinum blond hair for a Broadway role, joked: "Every time I try to push Julie into doing a full-blown erotica film. That's what I want to do, is just where Jesse and Celine, we really push the boundaries of cinema in a pornographic way and really explore all their relationship."
Delpy rolled her eyes and quipped: "In the seventh part, when I'm 80."
Hawke said it was rare to have such a close rapport with his opposite number from the first day of shooting.
"Usually when you have to play a romance you're like meeting the actress two days before shooting and we've known each other for almost 20 years now," he said.
Delpy chimed in: "We're not afraid of touching each other."
The Berlinale runs until Saturday.