Mendis, returning to the side following injury, took two wickets in his first over went on to surpass his own record of figures six for 16 against Australia in 2011.
Mendis’s name sake Jeevan Mendis took three for 24 as both spinners bamboozled the Zimbabweans who were skittled for just 100 in the Group C match.
Zimbabwe could never cope with Mendis’s unreadable deliveries and they collapsed like a pack of cards in pursuit of the daunting target of 183 set by Sri Lanka at Mahinda Rajapaksa Stadium.
Sri Lanka, who lost the toss and were sent into bat, owed their total of 182-4 to Kumar Sangakkara (44) and Jeevan Mendis (43 not out), who shared a 94-run stand for the fourth wicket.
Ajantha Mendis struck two blows in his first over, removing Vusi Sibanda (11) and Zimbabwe skipper Brendan Taylor (0) off successive deliveries. He next had Zimbabwe’s top-scorer Hamilton Masakadza (20).
He returned for his second spell and took four more wickets to end any lingering Zimbabwean hopes — and improve his own international Twenty20 record figures of 6-16, set against Australia at Pallekele last year.
Jeevan Mendis took 3-24 to cap an all-round performance.
Sangakkara, the newly crowned ICC player of the year, hit a 26-ball 44, studded with a six and two boundaries, while Jeevan Mendis smashed four boundaries and a six during his unbeaten 43 off 30 balls.
Both the left-handers lifted Sri Lanka from 82-3 after they were put into bat.
Tillakaratne Dilshan hit five boundaries during his rapid 39 before he fell caught behind by Taylor off leg-spinner Graeme Cremer. Skipper Mahela Jayawardene was run out for 13 while debutant Dilshan Munaweera made 17.
Twelve teams competing in the event are divided in four groups, with the top two teams advancing to the Super Eight stage, which will decide the four semi-finalists. Australia take on Ireland in Group B while former champions India face Afghanistan in Group A — both matches in Colombo — on Wednesday. Sri Lanka are bidding to end their 16-year wait for a second major title after winning the 50-over World Cup in 1996.
Zimbabwe won toss
E M D Y Munaweera run out 17
T M Dilshan c Taylor b Cremer 39
*D P M D Jayawardene run out 13
†K C Sangakkara run out 44
B M A J Mendis not out 43
N L T C Perera not out 6
Extras (b 4, lb 6, w 7, nb 3) 20
Total (4 wickets; 20 overs) 182
Did not bat: A D Mathews, H D R L Thirimanne, K M D N Kulasekara, B A W Mendis, S L Malinga
Fall: 1-54, 2-75, 3-82, 4-176
Bowling: Jarvis 4-0-31-0 (1nb, 1w); Vitori 3-0-27-0 (1nb, 3w); Utseya 4-0-25-0 (2w); Mpofu 4-0-49-0; Cremer 4-0-27-1 (1nb); Chigumbura 1-0-13-0 (1w)
H Masakadza b B Mendis 20
V Sibanda b B Mendis 11
*†B R M Taylor st Sangakkara b B Mendis 0
E Chigumbura b B Mendis 19
C R Ervine st Sangakkara b B Mendis 10
M N Waller lbw b B M Mendis 0
A G Cremer b B M Mendis 17
P Utseya c Jayawardene b B Mendis 1
K M Jarvis lbw b B Mendis 0
B V Vitori not out 7
C B Mpofu c sub b Malinga 0
Extras (lb 9, w 6) 15
Total (10 wickets; 17.3 overs) 100
Fall: 1-37, 2-37, 3-43, 4-58, 5-58, 6-80, 7-87, 8-87, 9-93, 10-100
Bowling: Kulasekara 3-0-16-0 (1w); Malinga 2.3-0-20-1; B Mendis 4-2-8-6; Mathews 2-0-7-0 (1w); Perera 2-0-16-0; B M Mendis 4-0-24-3 (3w)
Result: Sri Lanka won by 82 runs
T20I debuts: E M D Y Munaweera (Sri Lanka); B V Vitori (Zimbabwe)
Man of the Match: B A W Mendis (SL)
Umpires: I J Gould (England) and R J Tucker (Australia). TV umpire: R A Kettleborough (England). Match referee: J J Crowe (New Zealand)