Mathews at the heart of the battle
Rangana Herath rarely opens the bowling but the pot-bellied left-armer took the second over with Sri Lanka eager to hit England with spin early. His first ball was just what Sri Lanka ordered, turning past Alex Hales' outside edge to suggest an ordeal ahead.
England treated Herath with great respect, the first loud blare of the bugle coming midway through his third over when Jason Roy deposited him over long-on for six.
The captain's tumble
Joe Root's mistimed loft against Dushmantha Chameera just cleared Angelo Mathews at mid-off and the Sri Lanka captain's turn and chase could have resulted in injury as his vain attempt to save the boundary sent him crashing into the advertising hoardings.
The absence of DRS has not allowed too many umpiring errors, or led to too much dissent, but Roy's expletive after he fell lbw to the legspin of Jeffrey Vandersay was one sour moment: Rod Tucker's decision was validated by replays even though Roy was struck on the thigh.
Eoin Morgan has had a lean tournament and had only 7 from eight balls when he got a gift from Thisara Perera which he flicked behind square for four. The next ball flew straight over long-off for six. Perera was pulled from the attack after one over.
Jos Buttler's 28-ball 50 gave England's innings the impetus it needed. Dasun Shanaka was playing his first game of the tournament and came on to bowl the 18th over - a tough ask, as Buttler's straight six to reach his half-century testified.
Buttler's 97m six in the 19th over against Chameera was one of the longest of the tournament so far, a cross-batted smear from outside off into the top tier of the stand over long-on.
Mathews entered the fray at 15 for 3. Within one ball it was 15 for 4 as he pushed into the off side, changed his mind on a single and caused Lahiru Thirimanne to be brilliantly run out by Ben Stokes. To battle back from that was quite something.
The charge II
Sri Lanka needed 105 from nine overs when Mathews opted to go high-risk against Adil Rashid's legspin, including a last-ball six bludgeoned over long-on. England's spinners had anticipated rich pickings in Delhi, but the pitch had been watered to hold it together and four overs from Rashid and Moeen cost 63 - Matthews getting 39 of them off 14 balls
The hobbling hero
That Mathews had tweaked a hamstring was evident when he reached his fifty and needed treatment on the field. From that point, his running between the wickets was increasingly laboured, as two runs in the following over from Moeen Ali testified.
Chris Jordan justified his reputation in the England camp as a fine death bowler with his best figures in T20 cricket. The ability of Jordan and Stokes to deliver the yorker under pressure carried England home - with Jordan's final ball a good example, as Herath's stumps were demolished.
David Hopps is a general editor at ESPNcricinfo @davidkhopps