(Reuters) - Sri Lanka opener Kusal Mendis compiled a stroke-filled 54 to set up a commanding 33-run victory for the former champions in a warm-up match for the T20 World Cup against Zimbabwe in Melbourne on Tuesday.In the day's other warmup at the same venue, Ireland suffered a spectacular collapse against Namibia to go down by 11 runs in a low-scoring match.Dasun Shanaka's Lankan side arrived for the current edition in Australia buoyed by their Asia Cup triumph where they lifted the title ahead of powerhouses India and Pakistan, rekindling hopes of repeating their 2014 success in the T20 World Cup.Their indifferent form in bilateral T20 series earlier in the year have meant Sri Lanka have to play in the qualifying stage where eight teams have been split into two groups with the top two from each progressing to the Super 12 stage.On Tuesday, the opening pair of Mendis and Pathum Nissanka gave Sri Lanka a rollicking start with a stand of 57 in just five overs to set the platform for a big total.Mendis hit six fours and three sixes in his 29-ball knock and with some lusty hitting from Wanindu Hasaranga, who made an unbeaten 37 off 14 deliveries, helped Sri Lanka to a total of 188 for five from their 20 overs.Zimbabwe also made a brisk start to their chase by accumulating 39 runs in just three overs but it proved too steep an ask as Sri Lanka's bowlers found their line and length.Off-spinner Maheesh Theekshana and seamer Chamika Karunaratne picked up two wickets apiece as Zimbabwe managed 155-5 in their innings.Opting to bowl first in the day's second match, Paul Stirling's Ireland side restricted Namibia to 138-4 and then appeared in prime position to chase down the target by reaching 65-1 at the halfway stage.But Namibia