Hardik Pandya bagged three wickets while Jasprit Bumrah claimed one as Sri Lanka registered their second lowest total in one-day internationals, lasting only 92 balls.
India needed 6.1 overs to achieve the target for a timely boost before their home World Cup beginning next month.
"It's like a dream," Siraj, who became only the fourth bowler to take four wickets in an over in ODIs, said after the Sri Lanka innings.
"I got four early wickets last time I played Sri Lanka (earlier this year) but unfortunately I could not register a five-wicket haul.
Bumrah removed Kusal Perera in the first over to trigger a collapse and the Sri Lanka batters looked helpless as Siraj breathed fire with the new ball.
Persons:
Mohammed Siraj, Siraj, Pathum Nissanka, Sadeera, Charith, Dhananjaya de Silva, Hardik Pandya, Jasprit Bumrah, Kusal Perera, Kusal Mendis, Dushan Hemanta, Rohit Sharma, Ishan Kishan, Shubman Gill, Kishan, Gill, Chris Silverwood bemoaned, Amlan Chakraborty, Ken Ferris
Organizations:
Asia, Sri Lanka, Sri, Thomson
Locations:
COLOMBO, India, Sri Lanka, Australia, Chennai, New Delhi