Big picture
A T20 World Cup is around the corner. For Sri Lanka, it begins with the qualifiers, which kick off approximately six weeks from now. For South Africa, who go straight through to the main draw, the World Cup starts about a week later. Either way, this is the lead-in - the phase in which teams look to tighten up their combinations, get key players into form, and battle-test their match-ups and strategies. South Africa's eight T20I wins to their seven losses this year suggests they are closer figuring out a good game plan than Sri Lanka, who have lost six and won only three (two of those wins were against a severely depleted second-string India side).
South Africa are not only fresh from a series win against Ireland (whom Sri Lanka will face in the qualifiers), but had even defeated West Indies in the Caribbean in June and July. In Aiden Markram and David Miller, they have batters that have scored heavily in the format in 2021; in Tabraiz Shamsi they have a wristspinner who has claimed 24 wickets at an economy rate of 5.32. No other bowler has more wickets than Shamsi in T20Is in 2021.
Sri Lanka will feel they have some momentum after their ODI victory, but their T20I ranking of ninth is deserved - this is the format in which they have struggled most over the past few years. They will hope that the confidence gained from two consecutive series victories in a row (the first being that T20I series win over a depleted India), and familiarity with the conditions - which again are expected to be spin-friendly - can help elevate them to South Africa's level.
Form guide
(completed matches, most recent first)
Sri Lanka WWLLL
South Africa WWWWL
In the spotlight
Do Sri Lanka have a new Ajantha Mendis on their hands? On Tuesday, Maheesh Theekshana unveiled his well-disguised carrom ball and his googly at the international level, claiming four wickets - a record for a Sri Lanka spinner on ODI debut. Those figures, however, came on a deck that offered substantial turn. Can he be as effective on less spin-friendly surfaces? And now that South Africa have had a chance to analyse footage, how much of his mystery will Theekshana retain? In 14 bowling innings this year, only once has Tabraiz Shamsi gone wicketless. Of those innings, only in one - when Babar Azam hit full tilt in Centurion - did Shamsi go at more than eight an over. These are not just good statistics, they are performances that have elevated Shamsi to the top of the T20 rankings, one place above Wanindu Hasaranga from the opposition. Having already taken eight wickets in the ODIs, the T20s look set to see more Shamsi magic. There will be no bowler Sri Lanka will spend more prep time working out how to defuse. Pitch and conditions
Expect another turning track. With showers frequently rolling through Colombo, rain interruptions are on the card too.
Team news
Kusal Perera is likely to return to the Sri Lanka XI, after regaining match fitness following his bout of Covid. Kamindu Mendis will probably stat at No. 3, given his excellent T20 domestic form recently. Sri Lanka may think about bringing in offspinning allrounder Ramesh Mendis to bolster the lower middle order, too.
Sri Lanka (possible): 1 Avishka Fernando, 2 Kusal Perera (wk), 3 Kamindu Mendis, 4 Dhananjaya de Silva, 5 Charith Asalanka, 6 Dasun Shanaka (capt.), 7 Wanindu Hasaranga, 8 Ramesh Mendis, 9 Chamika Karunaratne, 10 Dushmantha Chameera, 11 Maheesh Theekshana
David Miller has recovered from a hamstring strain and is available. Lungi Ngidi, though, won't be, as he has flown straight to the IPL. Keshav Maharaj will captain the side.
South Africa (possible): 1 Janneman Malan, 2 Reeza Hendricks, 3 Aiden Markram, 4 David Miller, 5 Rassie van der Dussen, 6 Heinrich Klaasen (wk), 7 Wiaan Mulder, 8 George Linde, 9 Keshav Maharaj (capt.), 10 Kagiso Rabada, 11 Tabraiz Shamsi
Stats and trivia
South Africa have won seven, and lost five of their T20 internationals against Sri Lanka.
Sri Lanka's two T20I wins over India came after a five-match losing streak. Their previous win, over West Indies, had come after an eight-match losing streak.
In 12 bowling innings since the start of 2020, Wanindu Hasaranga's economy rate is 5.8. He has taken 21 wickets in that time.
Quotes
"Performance is everything, so we want to come here and win the series, to go to the World Cup with a log of confidence. What we've gone through in the last couple of months have been huge stepping stones for our T20 team. Beating West Indies - a lot of people thought we were underdogs. We won 3-2. A lot of confidence has been taken from that."
David Miller on South Africa's form
Andrew Fidel Fernando is ESPNcricinfo's Sri Lanka correspondent. @afidelf