Chelsea have completed the signing of Southampton midfielder Romeo Lavia, continuing their big spending this summer transfer window, the club announced on Friday.

Sources have told ESPN that Chelsea will pay an initial £53 million ($67.5m) with a further £5m ($6.4m) in performance-related add-ons.

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The deal takes Chelsea’s summer spending past the £300m mark, having last week signed Colombia midfielder Moisés Caicedo from Brighton for a British-record fee of £115m.

‘I’m really happy join Chelsea and be a part of this exciting project. It’s an amazing football club with a great history and I’m really excited to get started,” Lavia said in a statement.

‘I can’t wait to meet all my new teammates and build a chemistry together to achieve great things together.”

As with Caicedo, Chelsea beat off competition from Liverpool to secure the arrival of Lavia.

Liverpool had previously had a £60m offer for Lavia accepted by Southampton but the player expressed a desire to join Chelsea, allowing the the Blues to negotiate a slightly lower fee.

Lavia, 19, only joined Southampton from Manchester City last summer, making 29 Premier League appearances, and repeatedly impressed in a side that was relegated to the Championship. He also made his debut for Belgium in a friendly against Germany in March.

Saints paid an initial £10.5m but are due to pay a 20% sell-on fee to City after agreeing terms with Chelsea.

Information from ESPN’s James Olley contributed to this report.