England Thursday gave a Test debut to fast bowler Sajid Mahmood.
The 24-year-old Lancashire quick, a cousin of rising British boxing star Amir Khan, came into the team following injuries to fellow fast bowlers Stephen Harmison (shin), Simon Jones (knee) and Lancashire team-mate James Anderson (back).
All-rounder Flintoff, who led England to a 1-1 Test series draw in India earlier this year, continued to captain the team in the ongoing absence of Michael Vaughan with a knee injury.
From their squad of 13, England omitted uncapped 30-year-old pace bowler Jon Lewis and Ian Bell.
Alastair Cook, who scored a century on Test debut against India in Nagpur in March as an opener, was batting at number three following the return of Marcus Trescothick to to the top of the order after the Somerset left-hander came home early from India for personal reasons.
Cook, fast bowler Liam Plunkett and left-arm spinner Monty Panesar were all making their home Test debuts in a youthful side where only Trescothick was aged over 30.
Sri Lanka gave a Test debut to Chamra Kapugedera, a batting all-rounder listed at number seven.
At the top of their order Jehan Mubarak was installed as an opener after Michael Vandort made a pair in the tourists' final warm-up match, a 10-wicket defeat against England A, at Worcester last week.
The decision to drop Vandort came a day after a report from Sri Lanka said veteran opener Sanath Jayasuriya was set to end his Test retirement and come to England in time for the second Test at Edgbaston staring May 25.
Off-spinner Muttiah Muralitharan, the cornerstone of Sri Lanka's attack, was playing in his first Test at Lord's.
England: Marcus Trescothick, Andrew Strauss, Alastair Cook, Kevin Pietersen, Paul Collingwood, Andrew Flintoff (capt), Geraint Jones (wkt), Liam Plunkett, Matthew Hoggard, Sajid Mahmood, Monty Panesar
Sri Lanka: Upul Tharanga, Jehan Mubarak, Kumar Sangakkara (wkt), Mahela Jayawardene (capt), Thilan Samaraweera, Tillakaratne Dilshan, Chamara Kapugedera, Farveez Maharoof, Chaminda Vaas, Nuwan Kulasekara, Muttiah Muralitharan
Umpires: Aleem Dar (PAK) and Rudi Koertzen (RSA)
TV umpire: Nigel Llong (ENG)
Match referee: Alan Hurst (AUS)